Thank you for your interest in the Herobrine plugin! I am aware of the issue that you are describing, but unfortunately, I have been unable to fix it so far. I am still actively working on attempting a fix, but so far, no luck. I apologize for the inconvenience. Currently, the only workaround to this issue is instead use Spigot 1.15.1 for your server. This is of course not ideal, but it is the only working solution at this time.
There is no command to make him move. It should just happen automatically. How long was your server running before you started having this issue? Did Herobrine leave his starting position, move around, and get stuck somewhere, or did he just never start moving?
Herobrine never left the position and is stuck at 0 -20 0 and the server was up for about 30 minutes before added and restarted all the commands work fine he just doesn't roam.