You may need to modify the print-ready files for the orders your receive.
Zakeke allows it via Orders > Click on the arrow to open the detail:
You see the details of the order and just click on Edit Print-Ready Files:
After clicking on Edit Print-Ready Files, Zakeke will display the customizer screen and it will be possible to proceed with editing the design:
Once you're done with the editing, click on Update Print Files to save the new design.
IMPORTANT: new print-ready files override the previous print-ready files and you will no longer able to recover them.