1) The first suggestion is the move forgeter. This is just gonna be an NPC that would let you forget a move. For reasonss like Last Resort speedrunning mons or the second reason I am making this post.
2) Ranch teaching. In Sword and SHield if you have 2 mons of the same species, like if one is shiny or a custom form like an alter form, then the custom form or shiny might not get be able to have egg moves usually unless there is something set up for it. Now, if the move forgeter get atted in, then this can be also added and breed egg moves onto custom forms.