For Attendances this is the example

check_in                       employee_id / .id    check_out
2019-07-05 09:00:00    4                             2019-07-05 13:00:00
2019-07-05 14:00:00    4                             2019-07-05 18:00:00

You need to set the field name in the header of the column.

For many2one fields

To import the external id of a related company, use:

parent_id/id

To import the database id of a related company, use:

parent_id/.id