There is a tensioner, on the back side of the block it's the largest hex head item on that end of the motor. Gotta pull it, look it over to make sure it's not busted. Check pricing on a new one as they are known to go out, might be worth doing. Anyway, you have to click the remainder together, then once it's all put back together you put the tensioner back in and smack it to "unlock" the tensioner.
It'll be more apparent when you've got it out. There's a position where it's held in, and then when you tap it the end comes out and tightens up the chain. Make sure you don't spin the motor backwards, timing chains don't do that well.