Our grandson parked his dodge truck in our yard a year ago. Tried to start today after charging battery and it started but blew black smoke. Check all belts and found the alternator belt does not turn. Seems like the alternator is frozen. Can this be fixed.

All things are possible, just not always worth the effort.
First, you need to find out what part is actually "frozen" and see what it will cost to replace that, hoping that's the only problem with the alternator... you may be able to spin it but now you find it won't charge.
Just replace the alternator and belt. You'll find peace of mind is priceless.

Yes. It's easy and inexpensive to rebuild alternators. The procedure will be similar to the link below:

https://www.askmehelpdesk.com/cars-t...ml#post2518522

Ensure it's not the water pump bearing that's frozen--this is more likely.