To allow your church Treasurer/Accountant to update billing information as well as print receipts for monthly charges they must first be added as a User or Admin to your contact list. Please note that giving your treasurer Accountant Access to the billing information does not give them access to other owner privileges, such as removing contacts, curating content, changing the subscription and more.
Once they are registered, log in to the Owner profile and select "Organization Settings" after clicking "My Profile" in the top right corner.
From this page, you can search by name or email to locate your Treasurer, then click "Select" next to their name. Confirm your action and they will be given access.
To remove them, simply click "Remove" listed next to their name and confirm.