The solution is simple. Just open it. Let me demonstrate the specific operation method below, hoping to help you.
The specific steps are as follows: (demo version: Tik Tok 24.0.0)
1. After opening Tik Tok, click Me in the lower right corner.
2. Then click ≡ in the upper right corner and then click Settings.
3. Then click Notification Settings.
4. Then click on the private letter and make a phone call.
5. This interface pops up. Turn on the following three switches to receive private message prompts.