Changed alternator/stuck in drive on dash but will shift from P to L on shifter

My fiancé changed my alternator after my car quit running and wouldn’t not crank back
up or would shut off as soon as I would try to drive it after a jump. So he replaced it and now the car will start fine but it’s stuck in park. The shifter will go from park to L but on the dash it says it’s still in park. It’s like it’s not going into gear. I had it towed from where I broke down to my house. It’s never done this. I’ve only had it for 3 years. I still owe money on it. He’s still trying to figure it out. We cannot find anything online about it. The only thing I can seem to find close to it is that maybe the computer needs to be rebooted or updated. He thinks the tow truck driver broke something but I watched everything he did and there’s no way he did anything. He pulled it off the truck had it in neutral and went to put it in park an turn it off but it wouldn’t go into park or the key wouldn’t come out. I finally got it into park an was able to get the key out. Help me please. We’re at a loss.