In ServiceNow, the value in the Number field is auto-generated. The value in this field can be manually changed.
Manually change the value of the Number field in System Definition in the Number Maintenance module.
Restore is able to save the Number field globally for all out-of-box and custom tables. With custom scoped application tables, the Number field is not restored for any record that previously existed. It is recommended to create a separate external ID field that the ServiceNow Number field can be mapped to.