Have a button on your form that will copy whatever record is the current record, the record with the triangle on the left side (or pencil if editing data), and copy that record into the table that is populating the second subform. Or just copy the needed fields to that second table. This would best be done with a query, selecting on the key value(s) of the current record. To reference the current record, all you need to do is use the syntax of Me!fldName1, Me!fldName2 etc. The active record is the record whos fields you are referencing when using this syntax. The only way to get at other records values is to make the other record the current record. Usually this is done by the user moving the cursor in the User Interface.
What I'm assuming is that you have all your equipment showing in the first subform, and you want to pick only some of that equipment for shipment, movement, or whatever. Therefore, you want a second subform to display this smaller grouping of your equipment, and in the form of this smaller group, you need to add some quantities or whatever. So you will be, I think, dealing with two tables, tblEquipment and tblEquipmentToBeMoved (or whatever name).
HTH
Vic