Hi,

If you are using odoo 13 and below, you can change the sequence format from the sequence menu under the settings in the debug mode. Keep the developer mode activated in the database and navigate to Journals menu under the configuration menu of accounting, open the journal for which you need to adjust the sequence.

Inside the Journal form, you can see two fields of the sequence, click and open the sequence, from here you can adjust the sequence as per the need.

If you are using odoo 14, you can do it as follows, using the Re sequence option:  

Thanks