The FIRST thing that the organization should do to reduce the risk of data exposure when modifying its system to enable acceptance of credit card payments is to conduct a risk assessment, because it is a process that involves identifying and analyzing the potential risks, threats, and vulnerabilities that may affect the system and the data, and their likelihood and impact on the business objectives and processes. A risk assessment can help to determine the current risk level and exposure, and to provide the basis for selecting and implementing the appropriate risk responses and controls. The other options are not the first thing that the organization should do, because:

Option B: Updating the security strategy is a result of conducting a risk assessment, but not the first thing that the organization should do. A security strategy is a plan that defines the security objectives, policies, standards, and procedures for the system and the data, and it should be aligned with the risk assessment results and the business requirements and expectations.

Option C: Implementing additional controls is a response to the risk assessment results, but not the first thing that the organization should do. Controls are the measures that are designed and implemented to prevent or reduce the occurrence or impact of the risks, threats, and vulnerabilities, and to ensure the confidentiality, integrity, and availability of the system and the data.

Option D: Updating the risk register is a part of the risk assessment process, but not the first thing that the organization should do. A risk register is a tool that documents and tracks the identified risks, their characteristics, their status, and their responses, and it should be updated regularly to reflect the current risk profile and exposure of the system and the data. References = Risk and Information Systems Control Study Manual, 7th Edition, ISACA, 2020, p. 108.