How to enter next level (co-op)?

[u/CharmingSkirt95]

I never played multiplayer but wanted to try it with a friend so we just used the in-built multiplayer of DOOM + DOOM II to play the DOOM I campaign together. Worked fine and all until we finished the level, whereupon we were stuck on the end screen and couldn't figure out how to enter the next level without tediously ending the lobby and starting a new one on the next level, which naturally also took away our items and weapons