As you may know already, there is no option for you to remove manually edited content in bulk within Google Merchant Center. But there is a way.
How?
To remove the manual edits for all products, go to the cog icon > data sources
The first thing we want to do is take a screenshot of your attribute rules and your supplement feeds that are connected.
Lets take a screenshot of our attribute rules (if you did not add any, skip this step)
Click on your primary feed > then click on the attribute rules tab.
Now screenshot all your rules.
Now lets take a screenshot of the supplemental feed setup. What is important here is to re-link the supplement sources that have your primary feed as used in, for me this is FeedArmy (GB, English)
Now you can delete your primary feed, and re-add your feed.
Apply all your feed rules and supplemental rules.
Now all your manual edits are removed from the products.