Oh i see, then my bad it’s a UI thing, so here’s the thing :
when you get the menu screen with the training selected, you can actually use A/D to select left and right to choose other missions (i’m sorry the arrows don’t really look interactible so i can’t blame anybody getting confused here :p)
Oh and that’s ok if you don’t want to try it again either ^^
i’m thankful you’ve at least gave it another chance, but in case you want to hope this helps and that this was the issue.