Continue with the engagement in order to meet the regulatory deadline, but highlight areas in the final report that might need to be revised in the future.

Ask that a senior member of the organization's IT department with the required systems expertise join the audit team to assist in completing the engagement.

Delay the engagement and inform the board of the situation, asking them to provide acceptable alternatives for completing the engagement.

Remove the planned engagement from the audit plan and explain to senior management the problems with moving forward without an auditor with the necessary expertise.