Power management for IC8 biking

Hi all, probably my question will appear stupide for most of you. I just started to use Zwift with a IC8 biking. The connection seems working well but still to not understand how I have to manage the power. Currently my power on my bike is not changing automatically, when Zwift is requiring more power, I have to increase manually on my bike. Is it normal? If yes, how do I know which level (0-100) I have to select?
Thanks in advance for your answer