An auditor is preparing to analyze a client's sales data for the entire fiscal year.
The data is extracted from two different systems: the primary ERP and a legacy billing system.
During the data preparation phase, the auditor notices that the date format from the ERP is 'YYYY-MM-DD', while the legacy system uses 'MM/DD/YYYY'.
Which data preparation technique is MOST critical to apply first to ensure the data can be merged and analyzed chronologically?