ACM doesn't provide managed renewal for imported certificates. To renew an imported certificate, request a new certificate from your certificate issuer. Then, follow the instructions to manually reimport the certificate into ACM.
Private certificate issued with the IssueCertificate API call
ACM doesn't manage the renewal of private certificates issued by calling the ACM Private CA IssueCertificate API. You can request a new certificate before the certificates expiration date from your CA.