Maia here, from the Content API Team. I hope you are doing well.
If you already have an existing Content API feed, then it is not possible to create a separate Content API feed as there would be only one Content API feed per merchant account.
Now, to insert products from the Content API’s perspective, you can use the products.insert method (refer to this link for more information) or you can use products.custombatch method:insert that allows you to insert multiple products at a time using a single API call (refer to this link for more information).
On the other hand, if you’re not familiar with the given options above (as they are intended for developers) and your merchant account is connected to a third party platform for which you bought a license or subscription, then I would recommend reaching out to the support team of the third party platform that you’re using and ask for their assistance on how you can upload/insert your products in your merchant account using that platform.
I said that because our team doesn’t have any access and visibility to any third party platforms and even though they are using the Content API to perform its tasks, the application may have additional functionality or behavior that we aren’t familiar with.