There is no “TEX” template provided by Scrivener. Check with whoever gave you that template as to how to use it. And you do not edit a *.tex document in Scrivener. You use Scrivener to create, write, edit, and then compile a .*tex file that you then use a LaTeX tool to make a document.
Create a new document based on the “General Non-Fiction (LaTeX)” template provided by Scrivener. at the top of the Binder in the new project, just above the “Draft” item, is a document with full instructions.
Repeating what I told you earlier today:
There also is mention of LaTeX in the “Scrivener User Manual”, but I’ve not used other than cursory looking. Instructions in the Template are best to get started, and then I just looked at the Text Settings in the template editing dialog boxes, and made my own LaTeX settings in a file compiled as part of “FrontMatter”.
It’s all in your control. No magic.