Error 'your Exchange account is already associated with another Salesforce login' on Outlook Integration

Note: These steps must be performed by your Salesforce administrator. If you don't see the options to do so, then kindly request your Salesforce administrator to perform the steps for you as it requires administrator access to set up.
 

Log in to the organization that your email address is mapped to and disconnect your username

1. Go to 

In Lightning Experience:  Setup | Administration | Email | Outlook Integration and Sync

In Salesforce Classic: Setup | Administer | Outlook Integration and Sync | Settings
 

2. Click on Let users access Salesforce records from Outlook and scroll down to the User Mapping section.
3. Locate your email address under the Exchange Email column.
4. Click on the dropdown action at the end of the row on the right and click on Delete from the dropdown menu.
    

These steps remove the Exchange email address mapping with another Salesforce Account. Now, go back to Outlook or OWA and try reconnecting using the Outlook Integration. 


See Also
Get Access to Salesforce in Outlook 
Revoke User access to 'Outlook Integration'
Use the Outlook Integration with another organization