I was testing the encounter builder with one of my players last night. I couldn't figure out how to end the encounter. Is there no way to do this? I tried using "restart" but it didn't reset initiative or anything. I didn't see an option to end the encounter anywhere after starting it.

There is no option there to end the encounter. Restart does not reset party or monster initiative.

There is no “end” to the encounter, you just back out of it. Restarting the encounter should reset initiative for you though.