VNC Server on Raspberry Pi - Not active - unavailable to use.

I am using a Raspberry Pi ( Rpi3 B rev 1.2) and I have set up the interfaces for VNC initially, and it was working fine. then I had to change the Hostname and the Password on the Raspberry and I noticed that after that change the VNC icon in the Taskbar at the top of the display was missing.

I am no expert on the RPi but I tried. few things including uninstalling the VNC server then reinstalling and rebooting the RPi etc but with no success, I still cannot see the VNC icon and when I try to access it via remote VNC it fails with the expected error that it cannot connect to the VNC device.

Any suggestions, please?

Thanks

JohnW