In order to enable TikTok monitoring for your account, you can either add a new keyword to monitor from the Mention Tracker box and make sure you tick TikTok in the data sources section.
You can also edit an existing keyword and just enable the TikTok Data source and save it. Make sure you don't change anything else in this case, so that you don't lose any of your existing mention data.
You can also add a TikTok profile from the Mention Tracker box, by clicking the + button and choose to Add a Social Profile, like you would add any other Social Profile:
Please note, that it could take up to one hour to get the initial TikTok results.