Help fan belt replacing for 81 buick skylark

Hi there I have a problem Trying to put a new fan belt on my 81 buick skylark
It has a v 6 engine with three belts the one for air conditioning ,I removed I can't
Figure out how to loosen the pulley at the rear so I can get that belt on .
My mechanic buddy told me there is a square hole on the pulley bracket that
You put in a socket wrench and turn but I can't find any holes at all any help
Would be greatly appreciated,thank