The first step is to get them to create and activate their own Bricsys account. Once they have a Bricsys account you can add them as a manager to your license(s). Steps to do this are:
Log into your Bricsys account, and then select Manage Licenses from the user dropdown.
Find the license you want to work with and then pick the pencil icon to the right of the license key to bring up the manager window
Select the ADD Manager option, then enter the email address of the manager you want to add.
They are now added as a License Manager.
If at any stage you want to revoke their access, you simply go into the license management page and pick the cross option by their name.