If only you told us what your network operator was, some of us could have just looked it up for you. But since you haven't your going to have to join to get it :winktonguein this thread - to avoid double posting ).
There are two answers at least. I can see two avenues for that question.
Where can you examine the MMS APN on your phone? Settings > cellular + SIM > SIM settings > toggle "Manual Internet APN" to ON > edit MMS APN
Where can you find the setting you need to configure your MMS APN? One method is through your carrier website. Alternately, use this site to find you country and carrier then use the values they provide by tapping "edit MMS APN" then inputting the values into the fields and selecting "save": World Wide Mobile Phone Settings
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