The documents you will need to replace your certificate of competency depend on the category that your certificate comes under. The two categories of domestic certificates of competency are:
Low complexity certificates of competency are:
High complexity certificates of competency are:
Your replacement high complexity certificate will have the same expiry date as your lost, stolen, or damaged certificate. If your certificate is due to expire soon, you should apply to renew it instead.
Links
[1] https://www.amsa.gov.au/qualifications-training/equivalent-qualifications-and-skill-recognition/equivalent-first-aid
[2] https://www.amsa.gov.au/forms/certificate-competency-application
[3] https://www.amsa.gov.au/node/1527
[4] https://www.amsa.gov.au/forms/certificate-medical-fitness-international-certificates