Try to do a find and replace over all files inside your website source code project with the editor or tool of your choice. (can avoid many manual replaces)
find http:// replace it with https:// re-upload everything if I’m not mistaken and your website is http free the exclamation mark should disappear even when some resources would show loading errors. (404,…
not https compatible)
To fix those missing resources errors you can manually delete each of those nodes in your source code.
With a bit of luck all works just fine after a first re-upload!