Pick up a melee weapon (or assing one in the loudout) then if someone is in melee range you select your pawn go to the inventory from there you can equip the melee weapon.

Watch out if your pawn is injured he can drop the ranged weapon if it is to "heavy" because of the injuris.

https://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=2226330302

set up loadouts and carry multiple weapons at once