Databases are owned by companies. To transfer ownership of a database to another company, use the ‘Transfer Database Ownership’ option on the Settings page on the General page under Database.
Make sure you are currently in the database you would like to transfer (confirm at the top of the Options page), then use the dropdown highlighted in the image below to select a company to which you wish to transfer ownership.
Note: You must be a user on databases owned by both companies for this to work. If you do not see the company for which you want to transfer ownership, then you are likely not a user on a database owned by that company. Getting access to a database owned by the desired company will fix this problem. You can view a list of a company's databases on the Manage Database page in Settings.
If you have any questions, please contact support and we can do help you with your database migration.