Open TikTok and sign in to your account
Tap Inbox at the bottom of the screen
Tap the message icon or New message button
Search for the person you want to message
Select their profile
Type your message in the text box
Tap Send
If you do not see a message option, check your privacy settings
If the person does not allow messages from everyone, you may need to follow each other or be approved first
You can also message someone from their profile if the message button is available