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In the MDE, open the records using the split-screen (open the record that you do not want to keep first, so that it winds up on the left).
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With both records open, go to “Record actions” and select “Merge & Combine”
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Check that everything looks the way you want and then click “ok”
Specifically: make sure that you have different MMS IDs in the 001 and 904 field.
Finally, make sure that the secondary record is set to “suppress”
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