Dosya yanlış dizine gittiyse, dün gece yedekleme yapmamış olabilirim.

Gittiyse comes from gitmek (to go).

It breaks down like this:

• git- = go
• -ti = past tense
• -yse / -se = if

So gittiyse literally means if it went.

In natural English, depending on context, it can also feel like:

• if it went
• if it has gone
• if it ended up

In this sentence, Dosya yanlış dizine gittiyse... means something like If the file went to the wrong directory...

Because the verb gitmek usually takes the dative case when showing destination.

The dative ending often means to or into.

• dizin = directory
• dizine = to the directory / into the directory

So:

• yanlış dizin = wrong directory
• yanlış dizine = to the wrong directory

That is why the sentence says Dosya yanlış dizine gittiyse: the file went to the wrong directory.