I am not 100% positive I understand your question.
In your document, you should use paragraph styles (such as Head 1, Head 2 or whatever). Then generate a TOC from those styles and apply a TOC style that you also create. For example, if you have used Head 1 in your document, you might create a TOC style called TOC Head 1.
You can put that TOC into the text frame that you created (or create a new one).
Does that answer your question? If not, please clarify, and I'll try again.
When you generate a TOC, you will have a loaded cursor that you can flow on to a page, creating a new text frame, or replace an existing TOC. The styles within an existing frame will have no connection to how the styles of the toc are applied. This style needs to be created beforehand. And then assigned in the TOC panel > Entry Style