@QBking77 gives an excellent video tutorial on how to unroot and/or unbrick your Nexus 7. What is the difference between unroot and unbrick? Say you have to return your android for some reason. In order to honor your warrant the tablet has to be in in its original state so “unrooting” it will put it back they way it was when you bought it.
If you managed to “soft brick” your Nexus 7, the poor device is stuck in a boot loop or presumably won’t boot up at all. At any rate, watch the video below for the solutions.