How can I 'check' the "custom fields" box from the Screen Options?

I am using the latest version of WordPress v5.3.2. I am trying to find out a way [through Code] to enable 'Custom Fields' by default, when on the Add/Edit Post/Page pages, at least for the one's already having some values added to the associated Custom Fields. I am using a different template file, for such pages/posts. Any help in this regard will highly be appreciated. Thanks