mdtechteam Hi,
Yes, The "manage" tab on being clicked should result in opening of "Dashboard manager" as also outlined in documentation. The same works as envisaged whilst replicating on local install
Some troubleshooting steps to try seeing if they help in resolving the relative issue :
1. Try disable 3rd party administrator modules/extensions one by one to see for conflicts
2. Check JavaScript Console for any meaningful errors
3. Try updated to Php 7x stable version