You don't have to do anything with it. Bettas nest when they are happy.
It will eventually go during water changes etc, or he might destroy it.
But then he may build one again
So very true. Many Bettas will build bubble nests iun their new homes but as the filtered tank can create bubble nest destroying water currents and as we destroy them unintentionally when e do water changes, many Bettas will just lose interest in building bubble nests because they know they are just going to be destroyed in a few days.
My old Betta Jazz used to sulk something rotten when i destroyed his nests, he tried building them bigger - about an inch think, or spread them out, was fun to see his designs as he always did them when no one was looking!