@Ray-de-light Reading the documentation that I think you’re referring to:
If you need to update a site that you created using drag and drop, update and rebuild your project locally. Then, drag the project’s updated output folder to the deploy dropzone at the bottom of the site’s Deploys page. This will start a new site deploy with the updated files. You can also use this functionality to manually update any site that is not connected to a Git repository.
I’m interpreting this to mean that the dropzone only appears/works for sites that are not connected to a git repository.
You mention:
I tried updating it from Github, but got so many conflicts that I was confused and eventually the live site was disconfigured.
Despite your confusion with it, this makes me think that your site is connected with a git repository, and thus that the dropzone won’t appear.
While I don’t know for certain, I’d imagine unlinking from the repository would make the dropzone available to you.
This big thread indicates that once upon a time you needed Netlify’s help to do that, but that now you can do it via the UI yourself with: