You have to create an M365 tenant first. It will be yourdomain.onmicrosoft.com .
Data in your VLSC account will be located in the M365 account going forward. (keys/media)
This is the first step in getting the two linked up.
Keep in mind that you are setting up the M365 tenant that your organization will be using going forward - not only for VL stuff but any M365/O365 services they may use in the future so you need to make sure your data is good - this isn't a throwaway type account.
You should use something generic for the initial account - M365Admin@yourdomain.onmicrosoft.com - or something like that that's not tied to an individual. After the tenant is created, you can create your account under that giving it Admin privileges.