To create new users in your White Label, you need to go to the Users > Create user section.
There, you will need to complete the creation form where you can also select which DSPs you want that user to be able to distribute their releases to.
How to select DSPs when creating a new user?
You will find in the last three options of the form:
Fingerprint DSPs allowed: You allow the user to distribute to DSPs with fingerprint (YouTube Content ID, TikTok, Facebook, Soundcloud Content ID).
Streaming DSPs allowed: You allow the user to distribute to DSPs that do not have fingerprint.
These boxes need to be checked if you want to add DSPs to the new user.