Shower Temperature Control Adjustment

I am trying to repeat a service that a plumber performed on my shower system.

An engineer came and fixed an issue with the hot water not reaching the correct temperature by installing a new valve. On completion he was unable to test the water temperature because other work was being carried out in the building which meant the entire buildings hot water was turned off.

Because of this, he said that he may not have set the tap in the correct position. When the water was turned back on later that day, as he had suspected, the water was not as hot as it should be.

Another plumber came out a few days later and adjusted the position of the tap, and the temperature changed. I was not there to test, and would like to adjust it some more.

I am not sure if it possible to adjust more, or how the system works. I have read the manual, and there are no instructions on how to do this. It looks like the metal clip can come out.

This is a Vado system as shown in the pic below. If someone has any idea what the plumber may have done when adjusting the tap, I would be appreciate the help. Or if you think there is another issue.

I have another bathroom and the temperatures are fine.

Thanks for any help