I'd recommend doing the "fake" multiplayer glitch for this trophy, which you can find how to do here:
https://pastebin.com/Jgf6vPeJBefore starting the round, make sure you vote for the Snowball version of Tumble in the vote menu. Alternatively, when you're creating the round, go into the Settings and set the game type to Snowball only.
Once in the round, you simply need to keep throwing snowballs at the other player until they fall off the edge. Pay close attention to where you're standing so that you stay on the topmost layer. Once the other player is knocked into lava, the trophy should pop.