You will need to provide more information. If you could provide more details such as the process you are following or the documentation or reference used, it would be very helpful for the community to provide a better answer.
I will leave this other Groups Post that can be used as a good example on how to post a more informational question and could have some hints for your issue.
I would also recommend trying to follow the official documentation for Export and import using BAK files, including the Best practices for importing and exporting data