There are a whole lot of YouTube videos on removing rear wheels and how to remove, FIND THE CAUSE OF THE LEAK AND REMOVE IT, and change the tube and replace and remount.

Unless you are proficient at using a patch kit, don't try to patch the tube. It will only leak. Practice at home on this a bit. Personally, I am so bad that I never patch tubes - they always leak. I just put in a new tube, which I buy en mass at www.nashbar.com on sale.

I've had 5 flats so far this season - since May.