Log into your account via web (can’t do this on app, I used the mobile site). Hamburger/menu button on upper right, click Account, on next page tap on the line you need to do this to. On the next page hit “change SIM.” On the next page it will ask if it’s a physical SIM or an eSIM. If you already have the eSIM on your phone but calling isn’t working, choose “physical” here (counterintuitive I know). Grab the ICCID for your eSIM from the about page in Settings, put it in the box on the following page, and continue through until it confirms it’s updated. After a couple minutes the line should work on your new phone and the old phone will drop to no service.