What values have you tried changing? Should be as simple as checking the box ‘Simulate Physics’ then whatever force you have “push” the player, like a projectile, ensure it has an impulse setting (impulse is for a moving object like a projectile.) The higher the impulse (which loosely is it’s velocity with an added force) the more the object gets “pushed” or moved by the instigator (see the First Person Template for an idea of how a projectile knocks back the blocks in the level using impulse.)
Also ensure that all relevant collisions are set to “Block” the proper type of object (i.e. Pawn “Blocks” Projectile and Projectile is set to “Block” Pawn.) For not projectile objects, simply using the right collision combinations should solve the issue (i.e. a low ceiling pushes the player off the moving platform if he doesn’t crouch under it.)