You could use physics materials and turn the bounciness up, this would however usually require that the character jumps on it. Right-click in project, create physics material, set values and then add it to the rigidbody (I believe).
Other than that, you may try a simpler setup first, to remove potential pitfalls. First get the trigger itself to work, i.e. you must set the collider to trigger, and use the correct actions, as well as correct components: rigidbody, colliders, and playmaker actions. If you use 2D, then all of these in their 2D versions, else, the standard ones (Unity was originally 3D only).
Next, remove a bit of complication and make a simple FSM and attach to player. First state listen to a key, get key down (tip as usual: in a real setup, you typically want to use button actions instead of keys, because they can be configured in input manager, but key down etc is good for initial setup and testing, as a kind of scaffolding). When the key is pressed, apply velocity upwards. Again, watch out, if you work in 2D, you need velocity2D and corresponding components.
If that works, you can tweak this easily, how much velocity, how high etc. Next, combine both. When the trigger is activated, you need to check that it registers the correct player object (with rigidbody on it, etc), and then simply copy over the state with the velocity that worked. Lastly, the makeshift FSM on the player can be deleted as the velocity is induced from the triggering object.
It’s always a good idea to break down the problem into simpler chunks and hook them up quickly, so you can test them rapidly, especially circumstantial designs (if player goes there, does this and that, then this and that needs to happen).
Hope that helps.