The Champion EXP points are distributed by farming on your leader and claimed on your two champions. (so the leader can't claim the exp points but can claim the coins) You will need to Participate in the event on your two champions to claim them in the event. Once you've started participating in the event you can open the event screen by clicking the star on the left side and clicking legion champion again and it should open up the screen to click on the coin shop and claim the EXP points. Hope this helps
