Assuming that you have the Dometic CT digital thermostat, you have to tap, not push, but tap the power/mode button multiple times to scroll through the modes. Tap once to activate or wake up the thermostat; tap again to enter fan mode - tap the up or down arrows to change the fan mode (Auto should be chosen for most applications); tap the power/mode button again to enter Air Conditioning mode - tap the arrows to set the desired temperature; tap the power/mode again to enter heat/furnace mode - tap the arrows to set the desired temperature; tap the power/mode one last time to turn it back to off.
This will work if you have the Dometic CT digital thermostat. Search this online for a downloadable manual. Here is a YouTube video of one being used. His may or may not have the same functions as yours but it should point you in the right direction for use. https://youtu.be/xrdBTnO0Bd4
If you don't have this model, then you'll have to share what it says or what it looks like for us to help you further. Good luck.