You can't, It is spring loaded and it adjust itself.
There is no Timing Belt. It has a Timing Chain ,, inside the Engine.
what size engine
Note:The drivebelt routing decal on the radiator shroud to help during drivebelt install * To replace the belt rotate the tensioner pulley clockwise to release belt tension * Remove the belt from the auxiliary components and slowly release the tensioner * Route the new belt over the various pulleys again rotating the tensioner to allow the belt to be installed then release the belt tensioner
1.4 Eight valve engine. The water pump is the timing belt tensioner on this model. you need to slacken the pump and rotate it to tension the belt.
You can change the serpentine belt on your Chevrolet trailblazer, by loosening the tensioner pulley. With the loosened tensioner pulley the belt will come off easily. Tighten the new belt with the tensioner pulley.
Automatic belt tensioner - if not enough pressure replace tensioner Belt has streched too big, and the Automatic belt tensioner is at its limit. The tentioner is how yo remove the belt, so you should feel its tention with your wrench.
Remove beltUnbolt tensioner and remove
standard threads
If it has a serpentine belt it should have an automatic belt tensioner If it doesn't have a serpentine belt then alternator should be the adjustment/pivot point
There is no adjustment on the spring / Tensioner. You either have the wrong belt are the tensioner itself is bad. Replace tensioner are belt.
it has a manual tensioner
You will need to loosen the serpentine belt tensioner pulley on your 2002 Chevrolet Avalanche. Slide the belt tensioner to the right. The serpentine belt will become loose and can be removed. Reverse the process to install the new serpentine belt.