how to activate characters

[Malice]

hello please help i am in the tomb and have baretta in my party but in the walkthru im told to make sure spark is active in the party for the tomb (for some bromium or whatnot) but i now realized i have no clue how to put spark in the party i press (esc) and see just the four (random, sarah, guanidia and baretta) so please tell me how i can switch up my characters and activate spark

[Indinera]

that would be the button A