If you ever tried to change the theme of your page through your phone you might have realized that there isn't an edit  theme button. The reason is that the window size on a phone is too small to fit the editor so it doesn't show up.

However I have found a work around! I will be showing you how to do it on fire fox because it's the browser that I use but if you find a similar option on your favorite browser please add it to the thread

Steps for Firefox :

• Go to your page
• Activate desktop site
• Go to Settings>Accessibility
• Deactivate automatique font sizing and set the size to smallest
• Come back to your page

And you should find an edit theme button. It worked alright with me, the ui isn't great but it is hidden for a reason. Hope this helped.

I found the solution in the settings of Google

this not work.