If you already have an account in SportID, just type your company's name on a search bar.
By picking your employer, you will be able to send join request: sidebar at the left, below.
Once the request sent, the administrator of your employer's group will get notified.
After that, an administrator should confirm your request and apply a compensation plan as well.
If you don't see your employer's name in the search, it means that your employer is hidden from the search and they have to add you as worker.