Editing sleep data

Most days my Apple Watch thinks I am core sleeping after I wake up in the morning. I'd like to edit it so that the historic data is more accurate.

I followed the advice on another thread , as follows: Open Health ➡️ Browse Tab ➡️ Sleep: Now Keep Scrolling Down Until you see Show All Data. Delete core sleep. Replace with new data.

This worked as far as deleting the core data but I can't see how to add the revised minutes. I'm now left with zero core sleep which is more inaccurate than the original! Thanks.