Hello. I have an old classical guitar with warped neck. strings height is about 1cm on 12. fret. much too high. this happened years ago when i put steel strings on a classical guitar (not a good idea). my question is how can i reset the neck back as it was? classical guitars have no trus rod.
You have to decide if the guitar is worth the effort and cost. This is not something you can likely do yourself but a combination of a neck re-set and removing the fingerboard to plane the neck and re-glue the fingerboard on might result in a playable guitar. It's unlikely you can do either so a professional would charge accordingly. Chances are it's borked anyway.

Just an outside chance that the body front has bellied up behind the bridge and sunk under the end of the fingerboard. In some instances this might have caused the internal braces to come unglued, if that's the case you might just about get away with having them re-glued.

Chances are you can buy a decent used instrument for less than the cost of fixing you're youthful error.