I can't find the Auto-tensioner on my 99 accord.

I think this is right, but…
Find someone to help you if you can. To help hold the new belt in place when you are putting it on.
Make a diagram of the way the belt fits over and around the pulleys on your car. Don’t thing that you are going to remember where it goes.
Locate the drive belt auto-tensioner on the upper part of the engine (see pic). The tensioner is an idler pulley, since it does not drive any accessory on your vehicle. Its only function is to give the belt its proper tension.
Insert a long boxed-end wrench on the auto-tensioner pulley bolt of the appropriate size (probably 14mm) and slowly turn the idler pulley to release the tension on the drive belt (you are not removing the bolt; you are turning the tensioner so you can get the belt off while you have it turned under pressure). If you have a 2.4L engine model (2.3 Vtec should be similar), turn the pulley clockwise; if you have a 3.0L engine model, turn the pulley counterclockwise. Slide the belt off any pulley located on the upper part of the engine while you have the tensioner under pressure; then slowly release the tensioner pulley and remove the belt from the engine.
Check every pulley run by the drive belt and make sure they are free of dirt, debris and built-up material.
Compare the old belt to the new one and make sure it is of the same width and configuration.
Install the new belt beginning with the crankshaft pulley at the bottom and center of the engine and work your way up to the last pulley; follow your notes or the routing diagram on the engine compartment. If necessary, ask your helper to hold the belt stretched next to the last pulley on the upper part of the engine. Using the boxed-end wrench, slowly rotate the auto-tensioner pulley in the same direction you turned it to release the belt. Then slide the belt over the last pulley, and slowly release the auto-tensioner.
Make sure the belt is properly seated between the flanges of every accessory pulley.