Restrict Network Access

I have faded spots and I am adding WiFi extenders. How do I restrict access by devices after adding the extension devices?

 

The extenders should have a setup pamphlet and maybe a disk. It wll show something similar to log on, enter admin name and/or password, set up wifi password, # of max device connections and security type (encryption). Some admin names and factory passwords are on the edge or sides or labels of the extenders.

See this for some easy reference.

https://www.lifewire.com/accessing-your-router-at-home-818205