I'm a self-proclaimed pro at fixing that situation in about 10 seconds. Way cheaper and safer than turning a single bolt, though you could end up doing that if you somehow screw this up.
1. With tension on the chain (pulling up), remove your block
2. Stick a long screw driver (or some other long rod that will allow you to see where you're sticking it) and rest it on top of the tensioner (the slider part)
3. While pushing gently on the screwdriver, gradually relieve tension in the chain until the tensioner drops down and pops in
4. Immediately pull up on the chain and remove the screwdriver
It should make a gentle "thunk" as it slides in and 9 months later you're a dad. I got so good at this, I started doing it for fun, even seeing how far out I could get it before I had trouble getting back in. As I recall, I eventually let the chain kinda fall into the hole and don't need a block anymore. When I first ran into this issue, it came WAY out, as in nearly dangling and I could see the spring... I think.
Obviously, these steps assume the tensioner deflected UP out of the housing, not down. If it went down somehow, you could try a bent coat hanger to pull from above; not sure about that. Another option is to remove the oil pump and push up on the tensioner from below while a friend works your chain from above.