The merge button allows you to combine a number of products or cards. To merge the records:

Search and highlight the two you wish to merge. Whether it be a Card or Product etc.
Highlight both from within your list view of the module you are in
Eg below in the screen shot of two cards being merged into one

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Click the merge action button in the ribbon
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A popup window will display asking you which row to keep.
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You need to select which one you wish to merge into
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Select one from the list and click on OK
The history of all the records can be retained. But the details for only one of the records are kept. You have to let the system know which one you want to keep

With respect to Cards, all the addresses, contacts, history will merge into the one card selected to merge into.

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