As there is a lot of in store pick ups to set to awaiting pick up, the method below makes it easier than manually selecting the order.
Download all advent pre orders from big commerce in the large order fomat
Use Excel filters, filter out and delete all shipping orders.
Use the attached document and edit the order numbers to the new numbers
Save file a csv
Click on Orders->Tracking Numbers in Big Commerce
Ensure to change the drop down at the top from "shipping" to "Awaiting Pick Up"
Select File and continue as per normal orders