How to reformat an external hard drive after time machine?

I have an external hard drive upon which I put movie files that I view through a Sony box (like the Roku box). I brought my MacBook in for a repair and connected the same external HD and used Time Machine to make a back up. It did reformat it in order to do so, but since the Sony box isn't a pc or mac I didn't think it would make a difference, but now the Sony box won't recognize HD. Is there a way to reformat it on my MacBook so that I can use it on the Sony box again, or do I need to reformat it with a Windows computer? I had no issues when transferring files only and using the Sony box.

If you give any instructions, please write them out specifically, don't just post "you have to partition it" and leave it at that. I am computer challenged when it comes to these things. Think instructions for a person one step above being vaguely aquainted with a Mac please. Thanks.