Assuming that the users in question will be indicating that they need to trigger a knime flow from within Google Sheets (updating a predefined cell for example), you could certainly have a knime workflow scheduled to run periodically on your machine that would read that value and determine if the update is needed.
These polling strategies aren’t the most efficient and they obviously aren’t real-time. Because this approach would be dependent on your machine being on and connected in order to execute, this would also not the most reliable. (This is why folks purchase Knime Server)
If this is not a mission-critical process, this may work well enough for your use case, but be aware of the limitations and pitfalls!