Head to the sources page from the bottom of the left hand menu
Click Connect an Organisation at the top left of the Sources page.
This will bring up a page like the following for Xero
or the following for QBO
where you can select the organisation(s) you wish to connect.
Choose the organisation you wish to connect, and then follow the on screen instructions. Once you're done you will be redirected back into Mayday, and the software will finish connecting. This can take a few moments, so please be patient!