Where to create a “jump to main content” link

I’m not sure how to add this link in GeneratePress. More of where to add it. I tried widgets, and customized and it didn’t work. Possibly because I didn’t put it in the right box.

This is for ADA compliance. I would like to also make it “invisible” to naked eye, but visible to screen reader. Thanks.

The page I need help with: [log in to see the link]