I recommend walking 10' out of the field and then casting spells. Use the Disengage action if you really have to.
Second best option is to force whomever is maintaining the AMF to make a concentration check. Which should be very easy, as they won't have any options like Shield to help them deflect your attacks. Check your Backpack for any obscure item that you might have picked up, like a pepper shaker, or perhaps that set of bagpipes that you just couldn't get rid of. You don't actually have to deal damage to force a check, just be sufficiently annoying.
If you have prep-time, remember that created undead aren't summoned undead! That means they can walk (or float, whatever) around in an AMF with relative impunity. Similarly, you could Fabricate a siege weapon. And there is also the good old "Throw a Reduced boulder at your enemy and let it grow back to normal size on the way down" tactic.
If you cannot escape, the help action to give advantage to the fighter is a good option. We can argue if it is poor design to not have any chance to escape. The other PCs should be cool with you fleeing- like the fighter facing a rust monster.
Need more information. Is this the spell anti-magic field, or a DM-created dead magic zone, or something else? How are you being forced to fight in it? Can you prepare in advance? How receptive is your DM to creative skill use, and what skills have you got? What class and level are you? (A 4th-level cleric can just pull out a mace and start cracking heads; a 15th-level wizard, not so much.)