Finally figure out how to do it. This needs to be made much easier. You have to go to the permissions tab (bottom) in Amber, add a new app, copy the bunker address, then go to npub.cash, click on "wallet" (top right), choose nip46, then paste the bunker URL here (this is totally unclear for anyone that is not familiar with this stuff). They should just have a "sign in with Amber" button.