Αν το κουμπί δεν είναι καλά ραμμένο, θα το ξεκουμπώνω και θα το κουμπώνω όλη μέρα.

This is the normal way to make an if-clause in Modern Greek.

• Αν = if
• δεν είναι = it is not / it isn’t

So:

• Αν το κουμπί δεν είναι καλά ραμμένο = If the button is not sewn on well

Greek does not need a special English-style tense shift here. A very common pattern is:

• Αν
  • present/imperfective verb in the condition
• θα
  • verb in the result

So the structure is very natural Greek.

Because θα here is followed by the imperfective form: ξεκουμπώνω, κουμπώνω.

That gives the idea of:

• repeated action
• ongoing action
• habitual action in the future

So θα το ξεκουμπώνω και θα το κουμπώνω όλη μέρα means something like:

• I’ll keep unbuttoning and buttoning it all day
• I’ll be unbuttoning and buttoning it all day

It is not describing just one completed unbuttoning and one completed buttoning.

That would use the perfective future, which usually points to single, complete actions.

Compare:

• θα το ξεκουμπώνω / θα το κουμπώνω = I’ll keep unbuttoning / buttoning it, repeatedly or continuously
• θα το ξεκουμπώσω / θα το κουμπώσω = I’ll unbutton it / button it, as completed actions

In this sentence, the speaker means the button is loose, so they will have to do it again and again. That is why the imperfective forms fit better.

Because το is the direct object pronoun, meaning it, and each verb takes that object:

• θα το ξεκουμπώνω = I’ll unbutton it
• θα το κουμπώνω = I’ll button it

Greek very often repeats the clitic pronoun with each verb in a pair like this. It sounds natural and clear.

Here το refers back to το κουμπί because κουμπί is a neuter singular noun, so the pronoun is also το.

κουμπώνω means to button / fasten.

Adding ξε- often gives the idea of:

• undoing
• removing
• reversing an action

So:

• κουμπώνω = button
• ξεκουμπώνω = unbutton

This ξε- pattern is very common in Greek, though its exact meaning depends on the word.

ραμμένο is the passive participle of ράβω (to sew), and it means sewn.

It agrees with το κουμπί:

• κουμπί is neuter singular
• so the participle is also neuter singular: ραμμένο

Compare the agreement:

• ο άντρας είναι ραμμένος
• η μπλούζα είναι ραμμένη
• το κουμπί είναι ραμμένο

So καλά ραμμένο means well sewn.

Because καλά here is an adverb, not an adjective.

• καλά = well
• ραμμένο = sewn

So καλά ραμμένο means well sewn.

If you used καλό, that would be an adjective meaning good, and it would not express the same idea. The sentence is not saying the button is a good sewn one; it is saying it is sewn well.

Because Greek often uses the accusative to express duration of time.

So:

• όλη μέρα = all day
• literally: the whole day

This is very common:

• δούλευα όλη μέρα = I was working all day
• σε περίμενα όλη νύχτα = I was waiting for you all night

No preposition is needed.

Repeating θα before each coordinated verb is very natural and very common in Greek:

• θα το ξεκουμπώνω και θα το κουμπώνω

This clearly marks both verbs as part of the future result.

In some contexts, Greek can avoid repeating markers when the meaning is obvious, but repeating θα is standard, clear, and often preferred. For a learner, repeating it is the safest pattern.

In the first clause, το κουμπί is the subject of είναι ραμμένο:

• το κουμπί δεν είναι καλά ραμμένο = the button is not well sewn

In the second clause, the same button becomes the object, referred to by το:

• θα το ξεκουμπώνω
• θα το κουμπώνω

So the sentence moves from:

• talking about the button
  to
• doing something to the button

Yes, Greek word order is fairly flexible.

You can say:

• Αν το κουμπί δεν είναι καλά ραμμένο...
• Αν δεν είναι καλά ραμμένο το κουμπί...

Both are possible.

The version in your sentence is the most straightforward and neutral: it introduces the button early, then says what is wrong with it. Other word orders may shift emphasis slightly, but the basic meaning stays the same.

Greek often expresses that idea without needing a separate word for on.

• το κουμπί είναι καλά ραμμένο naturally means the button is well sewn on

Because a button is something attached by sewing, Greek can leave that relationship understood from the context. So ραμμένο is enough here.