It’s great you want to help your dad! That said, most lenders won’t allow you to take over someone else’s car loan without assuming ownership of the vehicle.
If your dad’s lender allows loan assumption, you’ll need to go through an approval process similar to that of applying for a loan. The lender will look at your credit report and your debt-to-income ratio to make sure that you qualify for the loan terms. If you qualify, you’ll sign the loan contract and begin making payments.
If you’re not planning to drive the vehicle, you could simply give the money to your dad to use for loan payments. That way, he could continue to build credit with the loan with your help!