When you distribute with OFFstep, you're using a trusted platform for TikTok, and your music should be populating into the platform's library automatically. Make sure you're doing the following before you file a support ticket:
Select the correct account type: Commercial accounts are not able to use songs from the platform’s library. There are audio tracks available for this account type, but they’re all stock music. If you're an artist or label, you should be using a creator account on TikTok.
Utilize TikTok’s audio library: Use the audio tracks available in the platform’s library. This is especially relevant for creators that use video editing software. Otherwise, the audio might be removed from the video when TikTok's system recognizes the content’s “Original Sound” as a legally distributed song that is available in the platform’s audio library.