Si la zapatilla me sigue rozando el talón, tendré que cambiar el cordón.

This is a normal real future condition in Spanish:

• Si + present, future
• Si la zapatilla me sigue rozando el talón, tendré que...

It means the speaker sees the condition as possible and realistic: If the shoe keeps rubbing my heel, I'll have to...

Spanish does not usually use the subjunctive after si in this kind of sentence. So:

• Si sigue rozando... = correct
• Si siga rozando... = incorrect here

A very common pattern to remember is:

• Si tengo tiempo, iré.
• Si llueve, nos quedaremos en casa.
• Si la zapatilla me sigue rozando el talón, tendré que cambiar el cordón.

Seguir + gerund means to keep doing or to continue doing something.

So:

• sigue rozando = keeps rubbing / continues rubbing

More examples:

• Sigue lloviendo = It’s still raining
• Sigo pensando en eso = I keep thinking about that
• Me sigue doliendo = It still hurts

In your sentence, me sigue rozando el talón means the rubbing is continuing, not just happening once.

Here me means to me / my in the sense that the action affects the speaker.

• La zapatilla me roza el talón = The shoe rubs my heel
• literally, something like: The shoe rubs the heel on me

Spanish often uses an indirect object pronoun like me, te, le, nos when talking about things happening to someone’s body or things closely associated with them.

So me shows whose heel is being affected.

Compare:

• Me duele la cabeza = My head hurts
• Me he cortado el dedo = I’ve cut my finger
• La zapatilla me roza el talón = The shoe rubs my heel

This is very common with body parts in Spanish.

Instead of saying my heel, Spanish often uses:

• an indirect object pronoun: me
• plus the definite article: el

So:

• me roza el talón = literally it rubs the heel on me
• natural English: it rubs my heel

Spanish does this a lot:

• Me duele la espalda = My back hurts
• Se lavó las manos = He/She washed his/her hands
• Me torcí el tobillo = I twisted my ankle

Using mi talón is not impossible in every context, but me ... el talón is the most natural structure here.

Here rozar means to rub against, often in a way that causes irritation or discomfort.

In the context of shoes, it often suggests:

• rubbing
• chafing
• causing friction

So la zapatilla me sigue rozando el talón means the shoe keeps rubbing against the heel and is probably starting to hurt or cause a blister.

You may also hear related expressions like:

• Me roza el zapato = The shoe rubs/chafes
• Me está haciendo una rozadura = It’s giving me a chafe/blister rub

In Spain, zapatilla can mean different kinds of light footwear depending on context, including:

• trainer / sneaker
• slipper
• sometimes a light casual shoe

In this sentence, because of el cordón and rozando el talón, it most naturally means something like a trainer/sneaker/shoe.

Context matters a lot. For example:

• zapatillas de deporte = trainers / sneakers
• zapatillas de casa = slippers

So here, think of zapatilla as the shoe that is rubbing the speaker’s heel.

It’s singular because the speaker is talking about one specific shoe, not the pair.

That makes sense, because often only one shoe causes the problem:

• Si la zapatilla me sigue rozando... = If the shoe keeps rubbing me...

Spanish can be very literal here: one shoe, one lace, one heel being affected.

You could also say something plural in another context, for example:

• Si las zapatillas me siguen rozando... = If the shoes keep rubbing me...

But in your sentence, the focus is clearly on one shoe.

Yes. In Spain, cordón can mean lace, including a shoelace in the right context.

So:

• cambiar el cordón = change the lace / shoelace

Because the sentence is about one shoe in the singular, el cordón likely refers to the lace of that shoe.

A learner should also know that vocabulary varies across the Spanish-speaking world. In some places, people may use other words such as agujeta for shoelace.

So this sentence sounds very natural for Spain.

Yes, both are possible.

• me sigue rozando el talón
• sigue rozándome el talón

With seguir + gerund, object pronouns can usually go:

1. before the conjugated verb
   • me sigue rozando
2. attached to the gerund
   • sigue rozándome

Both mean the same thing.

The version in your sentence, me sigue rozando, is very common and easy to process.
If you attach the pronoun to the gerund, remember the written accent:

• rozando + me → rozándome

Tener que + infinitive means to have to do something.

So:

• tendré que cambiar = I will have to change

Here tendré is the future of tener:

• tengo
• tendré

This is a very common way to express obligation in Spanish:

• Tengo que irme = I have to leave
• Tendré que comprar otro = I’ll have to buy another
• Tendré que cambiar el cordón = I’ll have to change the lace

Yes, mainly the vocabulary.

Two words that feel especially useful for Spain are:

• zapatilla
• cordón

In Spain:

• zapatilla is very common for certain kinds of shoes, especially trainers/sneakers depending on context
• cordón can naturally mean shoelace

In other Spanish-speaking regions, the same idea might be expressed with slightly different vocabulary. So the grammar is general Spanish, but the word choices fit Spain very well.