For CSV import the file should be a list of asins and a header os “ASINS”.

example:

ASINS
B00E7JMHU6
B004HHNYA0
B002LSI254
B002LSI254
B00359F6NE
B003FST1Z4
B003LVY7X6
B003NURS3G
B003NURS5Y
B003PGRQ8U
B0040QDXEA
B0040QDXPY