Hello,
you can manually export the required data from the existing DB. And when you are importing to the new DB, make sure all the mandatory and required fields are filled in the excel as well. There are different videos available in YouTube as well for the reference in importing.
As far as I know, you have to create a script in case you want to migrate big data if not planning go with the excel option.

Hello,

I managed to solve the error by making sure that the data is correct in the excel file.

Thank you for your comment.

@Balagopal R, I case I need to move data from Odoo 13 to 15. Do I need first to move the data to Odoo 14 then to Odoo 15?

Thank you.

Not really. You can directly migrate data from 13 to 15

@Balagopal R

Thank you.