Update item

@fuller the best way to do this today would be to actually use the Start Event variable as a 'Default Value' for your form controls. For example, with this task form, I have the greyed out version for viewing, but if I want to update that data I would use a date/time control and set default value to the Start Event variable:

This will let me edit that controls value. And then I can use that form variable to pass back to the SharePoint site when the task is completed:

Hope that helps!

@butlerj Thanks! Works with Assign a task, but when I try to do the same with Assign to multiple the form variables are grayed out. Am I missing something or not possible?

@fuller so this is because with the multi-user task action the responses come back as a collection (essentially a container that hold all of the various user's responses within it). To get to the individual items within the collection you will most likely want to use a loop action and either update the item directly (if you have append enabled on your SharePoint item) or use the 'Create a text string' action to concatenate the results: