As many have already said:
1. Foilow trends. Do a quick research on trending tiktoks arounds your niche and do content matching the trend
2. Use the trending sound. TikTok categorizes content a lot, if you do a trending tiktok, use the corresponding sound and vice versa. If your content with this sound does not match the trend, your tiktoks wont be pushed.
3. Check if your tiktoks are actually pushed in your target audience. If you live outside the US, it's likely you wont be pushed in the US but instead in your home country for example. There are ways around it however.
4. No courses will guide you step-by-step in creating viral tiktoks, you have to kinda feel it yourself. The lesson that really matters is watchtime is key, so make your tiktoks engaging for users so they feel the need to watch it until the end.
5. Don't repost/use stolen content. TikTok knows. If you do, make sure you research heavily on how to extract metadata, stitch method etc. But I wouldn't recommend going this route because its not sustainable.
6. Make the content look natural, blend in with other tiktoks. If you do salesy tiktoks, people will know and won't watch it.
MAKE YOUR TIKTOKS PLEASANT & INTERESTING TO WATCH. Think of your background, color scheme, creating intrigue/drama, random props for additional interest etc.
Hope this helps.