How can set remediation Owner in certification definition

Which IIQ version are you inquiring about?

8.3

i just wanted to set one remediationowner for complete certification.

Did you try global setting:

Gear Icon – > Compliance Manager – > under Lifecycle section

Default Revoker :

You can try to add this through debug > CertificationDefiniton and in certification search for certificationRemediationPhaseEnterRule and reference it to a rule as below

 import sailpoint.object.Identity;

    // Get the remediation owner by name
    Identity remediationOwner = context.getObjectByName(Identity.class, "remediation_admin");

    // Return the identity who will own all remediation items
    return remediationOwner;