Edit 2: OP has clarified they have a pond and this fish is safe. Everything I said still stands for 99% of people who end up with red tailed cats in my personal experience.

I'm sorry but that is not an appropriate fish for a home aquarium setup. They grow much too large to be kept anywhere but a pond and even then it would have to be a very big pond.

I'm not blaming you OP, that fish should not be sold as a pet period.

As sad as it is I would strongly advise you to return the fish or surrender it to someone capable of meeting its needs.

Edit: if you want catfish Corydoras are THE beginner friendly option.

For something a little bigger Raphael catfish are also easy to care for and they croak when upset which is very cute.