You can’t adjust the temperature to a maximum of 42°C on your spa.
The maximum temperature is set in the factory to 38 or 40°C.
Although it is possible to set the temperature display to 42°C for health reasons, your SPA heating is limited to 38°C.
You can increase it to 42° by reading the following procedure
In case your product is out of warranty (more than 2 years), fill out the form (available here).
If your product is still under warranty (less than 2 years), fill out the form (available here), with your purchase invoice and a photo of the problem attached.