One of Ginger’s ears came up before the other too. They were both up for a week or so, then the first one to stand fell when she was teething. Now they’re both standing and I couldn’t be more pleased. Some people suggest taping the ears up, but I favor the message technique. I would message the fallen ear when you’re holding him or when he’s sleeping and give it a week or two. If it doesn’t come up over time you may want to look into taping them, but I bet your pup is a doll either way.
Good luck!