Q: Apple TV and MacBook Air

I have a MacBook Air with OS X Sierra and am attempting to connect it with a 3rd generation apple tv that has been updated and reset.  They are both on the same network at my school and they both work individually on the network but the MacBook Air is no longer able to see the ATV on the network.  Therefore, it does not allow me to mirror anymore.  I am in desperate need of a fix.  It all used to work until I updated OS X.  Does anyone have any ideas to help fix this?  I have spent over 10 hours with Apple Support to no avail......