How do I block something that added itself to my wifi

AVG Performance
3

Hello, Delano

We will help you in this.
Could you share the screenshot of it for more clarification? 
And did you receive any notification from AVG regrading this?

2

Hello, Delano

We will help you in this.
Could you share the screenshot of it for more clarification? 
And did you receive any notification from AVG regrading this?

1

Gemtek added itself to my wifi and I want to block it