Need help with pihole setup on AT&T router bgw320

So I've tried searching around and I can't seem to get the last crucial step to get my pihole to block ads on all devices. As far as I can tell you cannot change the DNS on an At&t router, but is there no workaround to that to have devices still pass through the pihole? Also mind you I'm not that expertised in this, only having watched a couple of pihole starter tutorials.