google sheets – Create a Unique Order Number From Existing column of values

I need to create a unique ID from an existing list of order numbers. Pls see the image below:
enter image description here

What I want is for the existing duplicate order numbers to be made unique by adding an extra digit to the end. At the moment for about 300 rows with different sets of order numbers, I make numbers form 1-300(or however long the list) & join the order numbers with that manually. That makes the IDs too long, I just want to add a digit to the end of each set of order numbers.