Find your child's bounty on Subsquare under our bounty #43. Open it and in the bottom right part, click on Claim - sign the tx.
Go to polkadot.js: First Select Polkadot AssetHub as a chain you want to work with.
Then go to Developers - Extrinsic and fill in the details that are on this picture:
A number of your child bounty can be found, for example, via Subsquare here, or from curators.
Keep in mind that bounty claims can be initiated by anyone. In some cases, curators might do it for you. Funds will always end up in the account added by curators.