The hot tub needs power 24/7 to run the pump on low setting which filters the water constantly. It's also needed to heat the water.
If someone does turn off the hot tub, here's what you need to know...
The left rotary switch controls the hot tub, the right rotary switch controls the sauna.
In this picture, both are turned OFF. Rotate the switch so the flat handle is vertical to be ON.
On being turned ON, the hot tub control panel will say "PRIMING" for a short period and then it is ready to use.
Now you're ready to check the temperature setting, have a read of the Hot Tub Controls page on this site.