How to make the logo visible on mobile devices?

In Flexile header to make the logo visible on mobile and tablet device you need to edit the header.

In order to do that please move to the site Dashboard >> Divi >> Theme Builder >> Edit the Header.

Move to the Wireframe mode >> navigate to the module named Menu.

In the Menu module setting navigate to the Content Tab >> Logo >> Click on the tablet or phone view >> change the logo here and save changes.