Go to the iManage Control Center, on the left nav you’ll see Configure – Applications, as follows: 

1. Open that and add a new application: 
 

2. Add or generate a clientId and continue: 
 

3. Add or generate a clientSecret and ensure to add the following RedirectURL endpoint: https://{{ShareDoPrefix}}/externalServices/replyFrom (Ensure not to add a trailing slash here). 

e.g. https://core1.sharedo.co.uk/externalServices/replyFrom