MKIII Timing belt adjustment help

[xAimz]

So i bought the car block machined and rebuilt, turboed, and he said he redid the timming on it, but while driving around 40mph like 2k rpm the car would jerk back and forth, he said the timing might be off,anyways whats the easyest way to do this, could some one give me detailed info, ive tryed searching ( found nothing), and looking tru my heynes manual(no luck again )