the display on the controls says FLO and will not allow the spa to run. What does FLO mean and how do I reset it to run the spa

The flo error is telling you that your pressure switch is not detecting enough water pressure through the unit when running, so it'll either not heat or shut down altogether.

If you can't get it to go away on it's own, turn off the main breaker for a few seconds then turn it on again, and see if that changes anything.

You didn't say what brand of control yours was using, or if it had a separate circulation pump (small pump that is used for heating and filtration) as opposed to a main jet pump that does it all...

Also, need to know if the pump is running at all when you power it up, and then it quits and gives you the flo error...

That will help.