Re-seeding tool is used to reset the record sequence number without skipping any number. Skipping of number happens when you delete a record and then add a new one. This tool will help you to avoid such situation.
User will have to choose the Module and then, Start Number will automatically populate the correct number. If you feel, it is good for you, then you may update the same. Once done, you may visit the module that was just updated and try adding a record. It should add with a correct sequence number.