I did this with my private widows pension, the forms are available online as in previous post and are quite simple to fill in
For the turkish side of things I took the forms to the translator lady behind Fethiye PTT and she did the translation got the tax forms and all the Turkish side of things done for me,she has done many before she told me.
incidentally they will only sign you as being resident for tax purposes from the date that your residency visa started, so if you have been here on a tourist visa you may not be able to claim rebate for before that date
I then returned the forms to the address in the Uk by Cargo so that it could be tracked, all the turks use this for sending important things by post, the Post office is not too reliable
It took about 5 months for them to process in the Uk