First you need to make sure your company details are complete.
Go to Admin > General details.
Make sure, the contact details etc. are all up-to-date.
In the section DAC7 settings further down the page, add the information for the Legal company name and HMRC Platform ID. The HMRC Platform ID will be provided during your HMRC registration for Digital Platforms.

If you would like to be notified by email when an owner updates any DAC7 information in their owner login, enter the email address in the field Emails to notify after owner changes DAC7 seller information.
You can enter more than one email address, separated by commas, if needed.