If you only want to update the tracking number to a single order, you can refer to this step
Step 1: Click in the order > Click the button ‘Edit‘ on the right top.
Step 2: Scroll to the status section and update the status to ‘Shipped‘.
Step 3: Scroll down and put the tracking number in the column of ‘tracking number‘, and click the button ‘SAVE&SHOW’/’SAVE&LIST‘.