In the Bill of Materials module expand all the way to the BOM level to expose the “Search For” panel in which you can change the “Find From” drop down to Inventory.
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This will show all inventoried parts as a result. You will see the warehouse the product belongs to in the grid.
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Highlight the part you would like to add to the Bill of Materials / Quote and select the shopping cart symbol to reserve.
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This will just place the inventory as “reserved”. If you need to clear reservations, see here. Otherwise, someone will need to Issue the Inventory to Order. See here for additional details.