Hello and welcome to Just answer.com, Super mechanic here. About your vehicle.
It sounds like the reverse band may have broken, however, most times the shop will want to rebuild it if it is taken apart, to replace the band, for warranty reasons. The band in question is # XXXXX in the diagram.
I have included the steps for checking and/or adding trans fluid to it in a PDF format that you can download at the following link as well, thanks