You can submit an application for a healthcare benefit through the website of the Dutch tax authority. A DigiD is required for this.
You will be asked some questions about your age, income, and marital status during the application process.
Additionally, you may apply for the “zorgtoeslag” for any prior years (if applicable).
You can inform the tax authority of any changes to your circumstances, like an increase in income, via the website, otherwise if there is any surplus in your healthcare allowance, you will be sent an invoice in order to pay it back to the government.