remove the tensioner, install gear w/chain. DO NOT REINSTALL THE TENSIONER AS-IS. Push out the center pin towards the chain side, install the tensioner body, reinsert the pin from the outside, then the spring and the cap. It works by both oil pressure and the spring, plus it ratchets so if it fails it won't leave you with a very loose chain. Tensioner removal may allow the spring to ratchet the pin forward. If you install in that position the chain will be a bit tight
and will shortly self destruct.
So, did you loose a washer???? If so and it made it down to the sump I don't see a problem unless you corner hard, causing it to move. If it's on a chain gear or guide something will turn to toast. After the tensioner is back on, turn the engine by hand first. Even that may not be enough if its halfway down and later falls onto something that moves. Find the washer: bright light, magnet if its steel, etc.