If I understand your question correct, I think there are mulitple ways of achieving what you want. One could be by using the object / action: Utility - Collection Manipulation / Collection Contains Value.
If:
Excel sheet 1 = Collection 1 (Your original sheet)
Excel sheet 2 = Collection 2 (The sheet with data that you wish to validate up against sheet 1)
You can make a loop with Collection 2 as input.
In the loop you use the mentioned action, and set it as following:
Collection = Collection 1
Column Name = (Name of the Column you want to search in Collection 1)
Exact Value = Collection 2.(The Column where your data is)
If you find a match, you can make the according logic afterwards (set a flag, write to a new Collection etc. etc.)
