Club 80-90 Forums

Hi folks, can anyone point me in the right direction if possible. My alternator belt on a 1.6td jx 89 multivan, has been squeaking having been replaced after engine rebuild. What is apparent is that the tensioner pulley under and to the left if the alternator pulley is slightly pissed and not in line with the other pulleys. I'm now seeing scoring on the smooth side of the belt and rubber dust. How do I straighten this pulley and how is the belt tensioned?.
Any ideas greatly received
Regards
Nigel