Q: Changing Network password on Time Machine

Hi.

I have used a Time Machine for back-ups since 2010.  Recently I changed the Wifii Network password, at home.  The Time Machine no longer is accessing the Network, and I don't know how to change it's settings so it can re-connect on the same network.  When opening AirPort Utility, I cannot click on the Time Machine, it says "Device not found", and only offers me the option "Forget this device".  Should I forget this device to begin the process again? 

I operate on a MacBook Pro, OS 10.11.6 (El Capitan).

Would appreciate your help.

Tim