Need urgent help pls?

i got a 40 gall tank with 2 swordtails, two platys and 2 guppies, after researching, i bought 2 small angelfish from my local fish store and put it in my tank, they seemed to be doing fine but after i came home from dinner and checked the tank, one of them has torned finned , i suspect it got into a fight and i seperated it and put some medicine, will that fish survive??? when i bought it form the store, it already had a broken whisker, what do i do now?