Before we start, I would recommend creating a test site using the free GeneratePress theme, unless you already have one, to try this, although I used a test site without a child theme and it worked fine.

First you need to go to "Appearance" on the dashboard and scroll down to "Theme Editor". On the right-hand site, at the top, you should see this:

Now click on(functions php) and you should see this:

The code I will give you later should be placed where shown :