When the shower is set at cold, the showering temperature is too hot, what shall I do?

The hot and cold supply connections may have been connected the incorrect way round, if this is the case, swapping the connections should resolve the issue.

You can also check the temperature control settings in the shower valve by following the instructions in the user manual to adjust the mixture of hot and cold water to change the temperature range to see if there is any improvement. 

If your shower has no warm range, but goes from very hot to very cold, it may be time to replace the cartridge valve. This is a relatively simple job but do contact a registered plumber if you prefer.