Thank you for all your suggestions but nothing is working for me. 
Can I simply create a shortcut for left and right locator positions instead of using my mouse scroll wheel?
Whilst I’m playing my keyboard with my right hand I want to simply change the range of the loop cycle by 1 bar at a time either forward or backwards using for example the back and forwards arrow on my computer keyboard!
And to Steve, I’ve searched everywhere for the key command ‘move loop 4 bars’ but it’s not in my list and I use the latest version of Cubase 10 Pro?
Many thanks again for your help.
Kind regards
James Colah