If it's the same as my 89 then yes. I think you're talking about the belt that comes off the crank and drives the water pump and the fan.
From the front of the engine there is a jockey-wheel to the left of the belt. This needs loosening, repositioning and re-tightened.
However if you're in there you may as well replace the belt. But then you need to remove the A/C belt. So you may as well replace that too. That has a jockey-wheel adjuster the same as the fan belt.