See https://community.apache.org/pmc/adding-committers.html for the official reference.

After you have accepted your invitation to become an Apache Kafka committer, there are a few housekeeping items required.

1. Sign and submit your ICLA to the ASF secretary
   1. Read instructions here https://www.apache.org/licenses/contributor-agreements.html#clas
   2. Download, print, and sign the ICLA
   3. Scan and email signed ICLA to secretary@apache.org
2. Wait for your Apache ID
3. ???
4. Add yourself to the committers on kafka-site