How do i add or remove units from battle preperations?

sorry if this topic has existed before.
Tool ; FEbuilderGBA

so i tried practicing making a rom hack by making a small rom hack, all went smooth until chapter 5 the empire’s reach, it comes with a battle prep but my custom eirika is not on the battle prep and artur and lute is in it (i skipped chapter 4 so they’re not supposed to be there) so how do i add/remove units from battle prep?

events → load units. Use other chapter events for reference, specially chapter 6 which is he one where erika’s party rejoins.