You could insert the SIM in the old phone, then go to Settings and search for “Access Point Name” or “APN.” Look there to see which APN is active (selected). Tap on that and take note of what’s entered in the various fields, then write the same exact entries in the /e/ phone. Pay attention to spaces, dashes, capital/small letters, dots, commas, etc.
Or you could call your carrier and have support talk you through it, but that’s more annoying.
Actually, you may not even need to insert the SIM in the old phone to see the APN settings, but I’m not sure.
When entering in the new phone, you’ll probably need to “Add” (or “+”) to create a new APN. You also may need to restart the phone.