You probably can’t.

There are several countries where interrail really isn’t worth it, although that is depending on what pass is held and how much it is used elsewhere.

This information is from 2 weeks ago.

https://community.eurail.com/travelling-by-train-65/train-in-turkey-completely-booked-for-a-week-5351

I sent him a message right after he posted that message but I didn't get a reply :/

There are very, very few trains running-and all for long distance require a REServ-you will not be admitted or thrown off if not. RES most be done at counter locally-your name comes on it.

BUT-even pre covid when there used to be more trains, it was also worthless-local fares are very cheap (as TRL falls and falls) so just buy normal ticket is cheaper.

Plus that the basic network in TR is by bus-thats what anyone uses. Or cheap flites

Trainturkey.org seems to have best latest info on what does run.

Hello!

I think this will more useful for new users: I have travelled in Turkey in April 2022 and the way I dealed with the reservations was the following: I bought the tickets full price on https://bilet.tcdd.gov.tr/ (there is even a youth discount) and then, once in Turkey, I went to the ticket office and asked to switch the ticket from the standard to the interrail/eurail typology (with the number of the pass) and they sent to my bank account the full refund (until 15min the departure of train, otherwise it is 80% refund which is still fine). This was the method that was suggested from the cozum@tcddtasimacilik.gov.tr customer service and it fully worked for us with this route: Istanbul-Eskisehir-Denizli-Selcuk-Izmir-Balikesir. The trains are super new and safe and they are investing abudantly on new lines. The route Eskisehir-Denizli takes very long but the landscape is wonderful. 

Thus, I highly recommend a interrail trip in Turkey but surely needs a bit of organization, but these informations can make it easier!

Good luck,

Andrea