How to convert a video sent via text to iPhone to mp4 or mov when on desk top

Someone sent video via text to phone - I sent it to my desktop but it so blurry it's worthless. How do I convert the 3gp video to the mov or mp4??? so I can actually see it.

It was an AT&T network / iPhone 12 that sent video to my SE phone. It's now on my iMac desktop (catalina)