No option to change Mobile Data APN on Verizon network (iPhone SE)

I'm trying to configure my phone to be able to put a European sim card in, and per their instructions I've tried to navigate to the Mobile Data APN (under the Mobile Data Network settings) and have found that the option to change the APN doesn't exist. I tried syncing my phone up to iTunes using a cable and adjusting the device settings there but there's no option for that on iTunes either that I saw. I have an unlocked GSM iPhone SE that is supposed to be usable internationally but there doesn't seem to be any way for me to put in any other SIM card unfortunately.