To add the banners (icons) you have to go to your wordpress administration panel
In this administration panel you will go to movies or series, depending on which language you want to add the icon.
Remember the configuration of languages of movies and series comes separately, you must configure them individually, if your site will have series and movies you must configure the language and its icons separately. That is, configure it twice, once in each one.
once in Movies or series you will see all the options of the menu, put the arrow of the mouse over the menu option “Links” and more options will appear below, these options are “submenus”.
In these submenus you will find the option “Languages”.
Choose languages and the created languages will appear, if you have not created any you can start with the main language of your site.
It will allow you to configure
Language slug (name of the language in the link, url)
Main language of this language (Can be none)
and at the end icon, which allows you to put an external link or upload your own icon.
For theme settings I recommend you to upload the banners that we have chosen as default, although for taste you could customize or change them, there is no problem, just remember they must be optimized to not affect the speed of your site.