In the Hub, click 3 dots on bottom right. Click Settings > Text Messages > Advanced (at the bottom). Scroll down to MMSC Settings and edit all fields as provided by your carriers.
Suggest that you take a screen shot before editing the fields in case that you have to go back.
Easy on every other, but not in the stl100-4 Verizon Block the ability to change every apn, not Just the mms but the internet too, the internet can change va engineering menu, but the mms not