The only fix is to set your friend's gamemode to survival mode whenever he's logs on, but if you want a automatic way of doing this, install the plugin "Skript", restart your server, after the server restarts, go to file manager, plugins, Skript, scripts and create a new file, name it what ever, open it, paste in the below and then save the file, after you saved the file, run "/sk reload <whatever you named the file>", now whenever a bedrock user joined, they should be put into survival mode, please note, I haven't tested this so it may not work, if it doesn't, let me know.
on join:
if player's name contains "*":
set player's gamemode to survival
else:
stop
Also, please post in Help next time please.