It is not necessary to cancel a PKIo SBR, or Automotive Authentication, certificate, as these certificates are not issued as a subscription. You pay per application or each time you choose to renew.
Do you no longer use these certificates? Then they can be revoked by following the steps below.
Revoke PKIo SBR certificate
How do I revoke a PKIo SBR certificate?
Revoke Automotive Authentication certificate
How do I revoke an Automotive Authentication certificate?
You can also let the certificates expire.