The next time you utilize a drive belt, timing belt, or timing chain, you’ll likely need to loosen a tensioner pulley 
to eliminate it. Following these general suggestions and specific instructions from your own owners manual or repair manual, your belt or chain will function for the life span of your car.
Toyota and various other timing belt tensioners are loosened by simply removing them from the engine. You need to slowly compress them in a bench vice and lock them with a pull-pin before reinstallation.
Hydraulic (not hydraulic-damped) tensioners are nearly always located in the timing case, mostly upon automobiles with timing chains, while some are used in combination with timing belts. Hydraulic tensioners are powered by oil pressure from the engine oil pump and may press on a tensioner pulley (timing belts) or pressure slipper (timing chain). You’ll likely need the year, make, and model information, and you may need to use special equipment for this sort of tensioner pulley.
Typically, a hydraulic tensioner needs to be “reset” and locked after removing it from the engine. Remove the lock only after the tensioner, pulley, or slipper, and timing belt or timing chain are installed and aligned.
The spring maintains tension, as the hydraulic damper keeps it from bouncing under load changes. This prevents timing belts and timing chains slapping and jumping teeth and retains drive belts from slipping and making noise. To loosen a drive belt spring tensioner pulley, refer first to the repair manual or owners manual’s specific year, make, and model details.
You might need a special tool, but many spring tensioners have a square hole, for a 3/8” or 1/2” breaker bar, or a hex or square protrusion for a wrench or socket. Using the correct tool, release tension on the belt. You’ll need to hold some spring tensioners while slipping on a new belt. Others may possess a locking mechanism, such as a hole for a locking pin or hex essential.
To loosen an NAI tensioner, loosen the locking nut or bolt, then back off the tensioner screw. Drive the pulley toward the other pulleys or components, loosening the belt.
Spring tensioner pulleys, as the name implies, make use of a springtime to hold tension on the belt. Most, if not all, springtime tensioner pulleys are NAI tensioners and include a hydraulic damper. They are more complex and costly but don’t require changes and are less prone to user error.