Reduce Bond

Run the parachainStaking extrinsic scheduleCandidateBondLess function extrinsic from the account you bonded your collator with and enter the desired amount to reduce from bond. Remember polkadot.js needs, the KMA amount with 12 decmals.
Wait for 7 days.
Run the parachainStaking extrinsic executeCandidateBondLess function extrinsic from the account you bonded your collator with to withdraw the expected KMA to the account.