For instances when you try to reinstall Collabspot Connect add-in but you are still getting the old version. Please check in your Outlook application if an add-in was installed in Admin-manage Add-ins. This means that all add-ins for Outlook are managed by your Office 365 administrator. 

The image below shows when an add-in is managed by your Office 365 admin. 

Check if your Outlook has Admin Managed Add-ins

1. Go to your Outlook application. Click the Store button then click on Admin-managed button. 

Note: If you are the Office 365 admin, you can install the add-in via the Admin Center by following the steps from this link