1. Turn your Form Workflow Plus Activation Off (a) and share the spreadsheet with your colleague (b).
2. Share the linked form with your colleague: Form => Edit Form => Add collaborators.
If you do not share the linked Form your colleague will get the following message when he tries to activate Form Workflow Plus:
"You must be editor of the Google Form to activate the add-on."
3. Give the new workflow owner Creator role on the Web App
4. The new workflow owner turns Workflow Activation On and takes over from where you left off.
Use a Chrome Incognito window if you are unable to turn Workflow Activation ON. From your Chrome menu: File > New Incognito Window