Avoiding repeated data in access

I have a download consisting of Customer Order (CO) data and Purchase Order (PO) data. For each PO, there are multiple COs. Each PO and each CO have a quantity and other related info associated with it. Because of the many-to-many relationship, when the data is downloaded and imported into access, a single PO# and related info will be repeated as many times as there separate COs associated to it. Therefore when I wantto sum PO quantities, Access will sum each occurrence. What’s the way to avoid that?