1. Download the lsdoctor tool from this kb : https://kb.vmware.com/s/article/80469?lang=en_US
2. If VCSA then use Winscp to transfer the zip to vcenter appliance else in windows vc copy and paste to destination vc.
3. Follow the kb and run the trustfixer option -t : python lsdoctor.py -t 
4. Now restart the update manager service. 
5. Access the update manager tab.