The "Complete" button in the data entry forms is a feature native to DHIS2 that is: 1) not related to the PEPFAR data approval workflow and 2) currently not required for the data approval and submission process.
DATIM saves data automatically after entry into each field (the field turns green when data are saved). There is no need to press "Complete" to save data entry progress.
Pressing "Complete" does not submit data within the "Data Approval" application.
Please also reference this overview of the DATIM Compendium Document that describes the "Complete" button in the context of data entry.