How can the option Preserve Customer IDs be used?
As an additional option, you can choose to Preserve Customers IDs on the step Entities Selection of Migration Wizard.
It means that the customer IDs will be migrated from the source to the target store unchanged. For example: if you have customer #12 on the source store it will be migrated as customer #12 to the target store.
Note: The option requires clearing Target store data first. Additional options are not included in migration price and are charged separately.