Top menu >> Import data 

You can use this view to find out if you imported the incorrect commission data or if you import the same data twice. If you want to trash all data that you imported for a supplier or for all suppliers you can also choose to trash some items on the Import data page

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Click View imports

Click View items for the supplier you wish to trash the item for. 

If you suspect you imported data twice for a supplier you can sort by supplier by clicking on the Supplier header. 

Click Trash these items