HELP HOW DO I CHOOSE AN OLD MYSTYLE CARD IN LIVE INFINITY

Relax its very easy

1. If you have not chosen a mystyle for the event you must do it first. You can't train old mystyle cards without first choosing a new one
2. Next, go to the event page and click on your idol's thumbnail
3. Finally, look for the dropdown which will allow you to change to the past event set of mystyle cards.