Multiple misfire code

This might be kind of long but I’m going to explain exactly what happened when my car messed up. The other day my boyfriend jump started someone and right after he did it the car started running badly, wouldn’t hardly go and was popping. We bought a code scanner and scanned the car for codes and it gave us the multiple misfire code. Well we were driving home and he kind of slammed on the brake and it started running fine for a while. It eventually started doing the same thing again and then it would start running fine for a bit. It kept doing that the next day too. But now it seems like since it started running bad again this last time it hasn’t gone back to running fine anymore it’s just constantly popping and doesn’t want to go when you step on the gas. So my question is, where should we start to try to fix this? And was it a coincidence that it messed up after he jump started someone? I can also post what the freeze frame data says on the code scanner if I need to. Thank you for your help with this.