In the extension /extensions/fast_checkout there is no possibility to set the fields or delete them, I believe that the modification must be done through a file manager on some file inside the fast checkout folder. can anyone give me some suggestions on which file to edit and how to do? thank you
All files that you can to change placed inside public_html/extensions/fast_checkout/storefront/view/default/template/responses/checkout directory.
You can try to change them, but we recommends to create a new template extension based on default template (try to use our "developer tools" extension and clone template as extension )
Then you can copy directory public_html/extensions/fast_checkout/storefront/view/default as new directory with your newly created template text id. And then you can enable your new template and feel free to change anything inside your's template tpls.
To see directory tree as example you can look on bootstrap5 tpls inside 1.3.3 release.
Regards