Ticket problems

Hi y’all! Seeing if I can get some help on here bc I’m freaking out. So my family is planning on going to Epic Universe this weekend, we’re flying in on Wednesday and booked our tickets for Saturday. But there’s a problem with the epic tickets. We bought one day tickets to universal studios for the 14th, but we had no idea that those tickets apparently do not work for Epic universe because you have to buy a two day pass?? Is there any way we could be able to switch our tickets to Epic universe on the day at guest services or will we just have to go to IOA? We did not buy them through universal themselves. Has anyone else been through this?