Assist Mode is not designed for automatic activities, therefore it is not available in Scenario Engine.
The feature you ask about belongs to Custom fights and Monster grind feature pack. The combat system is still in early beta and there are several critical updates that must be implemented before this feature becomes possible.
You can emulate this feature via a static sequence of keybinds, but this method would not be stable. So please be careful and do not leave Miqobot unattended for an extended period of time.
For additional information about open-world combat, please read this thread:
Asking the community: Thoughts on Open World Combat and User Protection
Thank you for your request!