Bad news, the LTE functionality test hack used to edit apns on S9 and older phones doesn't work anymore. But good news is, if you know your MSL (all 0's for unlocked), you can create new APNs. Just dial ##3282#, put in your MSL, click APN Settings, and create a new APN with the same settings as APN2 LTE ... internet, but add dun at end of APN type.
You cannot modify the APN once you save it, but if you make a mistake, go to general management, reset, reset network settings to remove the APN you added and fix any problems.
EDIT: Updating profile deletes the APN so you should get used to creating new APNs frequently.