When you created your org with Xchart you were asked to complete and agree to a Business Associate Agreement.
If you need a copy of your BAA for your records, and you are and admin on your organization you can access it as follows:
Sign into your account (this is only visible to org admins)
Select "Org Details" in the Admin section of the menu:
Scroll to the BAA section and you should see your BAA and a "Download" option: