Are the details that the second person adds, in the same app? or a second one.
To keep it a bit simpler, i would stay away from sending the data to Flow. Like you said, this is harder with multiple items and multiple columns.
If you have an ID column in the excel table, Why not pass the ID's to flow in the notification you send to the second person.
Then that person can look up the item in a gallery in the app, and edit it.
It won't be the prettiest option, but an option nonetheless.
If there are a maximum amount of items User 1 can create, you could also convert each row into a string and pass in to flow, so you get 1 string per row. This won't work if there is an infinite amount of rows user1 can create.