Testato,
If I understand you correctly, it is probably simplest to adjust the wiring rather than the code. Take a look at Arduino pins 10,11,12,13. Those corresponds to the digits.
Say right now you have it wired like this:
| Arduino | Display |
|---|---|
| 10 | P |
| 11 | Q |
| 12 | R |
| 13 | S |
You have complete control as to which digit value correspond to which display digit. What if you re-wire it like this?
| Arduino | Display |
|---|---|
| 13 | P |
| 12 | Q |
| 11 | R |
| 10 | S |
Good luck!