You can have a pap smear test done while on your period.
But it's recommended to wait until your period is over and you're no longer bleeding.
If you go get a pap smear test done while you're on your period then the Menstrual blood can cause inaccurate test results because the menstrual blood can obscure the visibility of the cervical cells collected in the sample during the pap smear test.
So to get the most accurate test results from having a Pap smear test done you should always wait until you're done with your period and blood is not flowing.
That way it makes it easier for the pap smear test to be done and provides more accurate results.