MetaLocator tracks the filename from which each record originated and you can search by that field to help isolate and delete a bad import.  To search for a specific source file, go to "Data > All Records".  Then, expand the Search & Select control as shown here:
 

Notice that in the above screenshot, we selected a specific Source File.  Once you have identified the source file you would like to isolate, choose it from the drop-down and click Create Selection. Once a selection is created, the Search & Select box will show "N records selected." to indicate that not all records are shown and a green message will indicate that there are records selected.
 

 Once you have selected the offending records, choose an operation from the Bulk Actions drop-down in the upper right.  A common strategy would be to choose Delete to remove the records.  Once you have removed the records you will want to clear the search filter (so you can see the rest of your data)  by clicking Clear as shown here:
 

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