The thin content penalty is perhaps the easiest penalty to recover from. It's very much in the name. Google thinks you are doing one of the following.
- Automatically generating content
- Doing heavy affiliate programs with little to no content
- Scraping your content
- Using doorway pages
Now let's go through the list
1 - A: This would insinuate you're using some form of spinning software. This is low quality, thank heavens most search engines can distinguish this from good content because it's spammy. The way to tackle this would be to write your own, good quality content.
2 - A: Having affiliate programs is absolutely fine. But you need to wrap them in awesome content, tools, or something that'll genuinely add purpose to the user.
3 - A: Scraping. Now, if you're scraping your content, the answer is simple: Stop.
4 - A: Doorway pages have been a big no-no for a while now. You're better off making one fantastic page opposed to 100 terrible ones. Read more about doorway pages here: https://seochat.io/question/doorway-page/112
I wish you luck - think quality, quality and quality.