I found a red round pill one side has an m the other side said 30 know what it is?

Are you sure it's an M, all I can find in round red pills with a 30 is a heart medication called Nifedipine, it has a 30 on one side and a B on the other, a small m can look like a B on its side.

Complete Nifedipine information from Drugs.com

If it's definitely an M than sorry, don't know.

Take it to a pharmacist they can identify it for yo.