You can do this via your database or via the system settings page.

Through Database
Using your database tool, for example, PHPMyAdmin, select your database, select the order_ref table and set the values of so, qu, po, etc to your own number, for example, 1.

The System Settings
Log in with the Owner account, navigate to the System settings page and scroll down to the bottom of the page. At the right side of this page, you will see Run cron job now button just below the Update Settings button. Click on it and the system cronjob will run and automatically reset reference no and as well perform other tasks.

In case you need a developer for any modification on the system, you can reach out to me at [email protected] or Skype ID enyinnayag or WeChat ID wxid_9o59xqufzhfd22.

I am an Independent developer that knows the system very well.

@Mian Saleem is aware of my presence here.

Thanks