Sorry if you feel that way, but all sites (files) resides on a server else the site won’t be up on the internet.
I believe what do you mean is you don’t have FTP access because the hosting (or your plan) does not allow, or is it? So that is why you’re using that Child Theme Configurator plugin, right? But we are not in the position to give instruction for that plugin because that is a 3rd party plugin and we are not familiar with it, it is better if you contact the plugin support. I think that plugin would not able to complete Ruenel’s instruction above because on step 4 you need to create a few subfolders (but again we are not familiar with that plugin).
I know you understand Ruenel’s instruction above, but that requires you to use FTP, you need to ask your hosting for FTP credentials if they do provide.
Please watch this video, this will give you idea how FTP works.
How to Use Filezilla FTP Client
If not, contact the Child Theme Configurator plugin support and show them Ruenel’s instruction and ask if that is possible to do with their plugin.
If still not, then you need to find a File Manager plugin, however this is not recommended, as one tiny mistake with PHP code can lock up your site, so again FTP is still the best thing to do this customization. If your hosting does not provide FTP credentials then there is nothing we can do about it.
Thank you for understanding,