Need some information or sources

Hello. I am not a reseller as most amazon seller users are that I’ve noticed and I am looking for insight on what could help me grow my business. I’ve had my private label products in Amazon for a good while now and growth is super slow. I’ve done basically everything there is to do (or it seems so) on amazon in general. The issue I have is that most of the content/guides/sources that is meant to help learn selling on Amazon is coming from and focus for amazon resellers. Alot of the information is on how to pick the right product blabla and sell it. The thing is I cannot pick my product I already have a product and I need to learn more ways on making it visible on Amazon. My product falls in a high contested category where keywords are very expensive to advertise. And mainly the first like 5 pages of products are filled with the same 2-3 brands that are very big already and not just on Amazon.

Does anyone have any sources I can learn from as a private business going to Amazon?

Thanks