This feature is available in Manage app data module of USM which can be accessed from menu bar on the top right of the screen.

Step 1. Click on the Manage App Data option from the menu bar.

Step 2. Click on the Manage code sequence on the left of the screen.

Step 3. Click on the modify option on the employee no bar.

Step 4. Click on the prefix or postfix option to change the sequence and then save the form.