Click Add Existing to select an existing part to add as a substitute for the
current part. The Search page opens showing only the components in the
context BOM.
Select the current BOM part that you want to substitute and click Done.
A second Search page opens, showing all valid parts in the database.
Select a part that you want to specify as the substitute part and click
Done.
The substitute part is added to the table.
If the part does not yet exist, you must first create it, then access
the Properties page of the part where you want to define it as a substitute.
For details on a creating a new part, see Creating a Part.