I have a one bedroom rental above my detached garage. It has separate meters for utilities so would I just list it as if it's a separate property or as if I'm renting out part of my house since it was

Yes, consider it rental of part of your home, because you will need to allocate property taxes, insurance, etc (in addition to the utilities) to this rental.

You will need to set up the rental under the Rental and Royalty section of TurboTax (Schedule E)