See
USB basics and troubleshooting.
If the two devices have different data in the fully-populated Virtualbox USB filter, such as serial numbers being different, then you can follow the USB Basics tutorial's advice to use only the VendorID and ProductID, then add one of the differing pieces of other data to the filter.
If the two devices have identical filter data and none of the data is different, then you can add the port number to the filter for the device you want to add to the VM. See
Distinguish multiple identical USB devices.