Here are the steps to enable a disabled plugin on Outlook 2013/2016:
1) Click on File > Info > and select "Slow and Disabled add-ins"
2) Enable Yesware for Outlook
Here are the steps to enable a disabled plugin on Outlook 2010:
Click on the "File" tab in your navigation
And then Click Add-ins
Try scrolling down in your add-ins list and see if Yesware Outlook might appear in any of the inactive or disabled lists.
Select YeswareOutlook from the list of disabled add-ins (if it's there) and click "Enable"