How do you adjust the belt for power steering on a 1986 Buick Regal if you do not see a pivot or slot for adjustment?

If you have a serpentine belt (this belt is flat on one side and has 6 little "v's" on the other side about 1 1/4" wide) then there should be an "Idler" pulley that is internally spring loaded that puts the required tension on the belt, thus there is no "adjustment". But if this pulley is defective it must be replaced.

If yours has a single big "V" belt (about 1/2" wide) then the "Adjustment" usually consists of loosening the alternator and "biasing" it to tighten the belt then securing it again.