How can I add custom Thumbnails to my custom Primary Data Asset that is also a plugin.

As the Title says. I want to add Thumbnails to my custom Data Assets and change its color as well. I had tried to follow all the tutorials I could find and I couldn’t do anything and get the result I want. People are saying create new Factory classes but that is only for custom UObjects from the looks and even still I cannot create it because it gives me some random errors.
Any help would be appreciated if they could be much simplified and detailed on where to go and so on…
Thank you!