Se la chiave magnetica non funziona, torno subito dalla receptionist.

Se means if.

This is a straightforward, real-condition sentence:
Se la chiave magnetica non funziona, torno subito dalla receptionist.
= If the key card doesn’t work, I’ll go straight back to the receptionist.

In Italian, when the condition is realistic or possible, it is very common to use the present indicative in both parts:

• se ... non funziona
• torno subito ...

English often uses present + will in this kind of sentence, but Italian does not have to use a future form here.

Because Italian often uses the present tense to talk about a future action when the context makes it clear.

So:

• Se la chiave magnetica non funziona = If the key card doesn’t work
• torno subito = literally I return immediately, but naturally I’ll go back right away

This is very normal Italian. You could also hear future forms in some contexts, but the present is extremely common and natural here.

Italian uses definite articles much more often than English.

So la chiave magnetica literally means the magnetic key, but in context it means the key card. In English, depending on the situation, you might say the key card or sometimes just the key, but Italian typically keeps the article.

Literally, it means magnetic key, but in everyday usage it usually refers to a key card, especially in hotels.

So in this sentence, chiave magnetica is the hotel card you use to open the room door.

Because funzionare is a normal verb meaning to work or to function.

So:

• funziona = it works
• non funziona = it doesn’t work

Italian does not say something like is working here in the same way English sometimes does. The simple form funziona is the standard choice.

Examples:

• Il telefono non funziona. = The phone doesn’t work.
• La doccia funziona bene. = The shower works well.

Because tornare means to return / to go back / to come back.

Here the speaker is going back to a place they were already at before, so torno is more natural than vado.

• torno = I go back / I return
• vado = I go

So the idea is not just I go to the receptionist, but specifically I go back to the receptionist.

Subito means immediately, right away, or straight away.

In this sentence:

• torno subito = I’ll go back right away

Its position is very natural here, right after the verb. Italian adverbs are often flexible, but torno subito sounds simple and idiomatic.

Because da is often used when going to a person, especially in the sense of to see / to speak to / to go to where that person is.

So:

• dalla receptionist = to the receptionist / back to the receptionist

This is da + la = dalla.

Compare:

• Vado dal medico. = I’m going to the doctor.
• Torno dalla receptionist. = I’m going back to the receptionist.

Using a here would sound much less natural.

Yes. Receptionist is a borrowed word used in Italian, especially in hotel contexts.

It is common in modern Italian, although you may also hear longer expressions like:

• addetta alla reception
• impiegata della reception

In everyday speech, though, receptionist is very understandable and common.

Because of the article la in dalla receptionist.

The noun receptionist itself does not change form here, so the gender is shown by the article:

• il receptionist = the male receptionist
• la receptionist = the female receptionist

So dalla receptionist tells you the speaker is referring to a woman.

Because the sentence begins with the if-clause:

• Se la chiave magnetica non funziona, ...

When the conditional clause comes first, Italian commonly separates it with a comma, just as English often does.

You could also reverse the order:

• Torno subito dalla receptionist se la chiave magnetica non funziona.

That version is also grammatical, though the original order is often clearer and more natural in context.

Not in standard Italian.

After se, in this kind of real condition, you normally use the indicative, so:

• se ... non funziona = correct

funziona is the present indicative.

A form like funzioni is a different mood and would not be the normal choice in this sentence.

Yes.

Because the present tense is used, the sentence can depend on context. It might mean:

• If the key card doesn’t work, I’ll go straight back to the receptionist.
  or
• If the key card doesn’t work, I go straight back to the receptionist.

So it can describe either:

1. a likely future reaction, or
2. a usual response in that situation.

In real conversation, the context normally makes it clear.