The "Reset" button should re-connect the GFCI part of the plug...that's its purpose. That being said, there may be a "lingering" bleed over on the main bus that is fooling the plug into thinking that it should still be tripped. Try turning all the master 120v circuit breakers off (in the mains housing) and then see if it will reset.
Sometimes the "Reset" button needs a firm push, more than some fingers can supply and you may need to use a rod or screwdriver to seat it deeply. I've seen some that seat fairly deep in its hole and even my little fingers couldn't get it deep enough to latch; a phillips screw driver did the trick.
The only other recourse would be to replace the plug... If you can't get the "Reset" button to re-latch in its housing, there aren't any "tricks" to get it to work normally again. It is a regular household type GFCI plug, nothing special about it for RV use.
My 2 cents, your mileage may vary...
2 Cats; J-Lo and Ragamuffin :R
2014 Thor Tuscany 40RX DP
2011 Ram 2500 Longhorn CTD HO
2011 Keystone Cougar 318SAB (now gone)
2008 FunFinder X 210WBS (Sadly gone)