Use trigger_catapult if you want to fling people into the air. Or push you you want a shove.
actually, trigger_apply_impulse might be better suited if there isn't a specific launch target, but rather just a direction (i.e. up). It needs to have an input of ApplyImpulse in order for it to blast anything, so what you can do is have it OnStartTouch send ApplyImpulse to the entity !self (that's the trigger itself).
Also, it's func_conveyer. It's not a trigger entity so it doesn't have any trigger functionality (i.e. no OnStartTouch, no !activator). In addition to that, it has difficulty pushing objects upwards (hasn't worked for me). It's more suited for an actual conveyer belt, where objects are pushed horizontally.
If you'd like you can check out a video I made on launching players. I didn't include func_conveyer since it didn't work for me to launch players upward.
Another option is to change the player's basevelocity with AddOutput. it basically does the same thing as trigger_apply_impulse, but it can be used on any trigger or even button. You can check out the text version of that tutorial here:
https://tf2maps.net/threads/the-input-named-addoutput.32687/