How to change old pay period?

Hi Soneeraj, 

Thank you so much for your question!

By old pay period, do you mean a pay run that you've finalised which has the incorrect date on it? 

If so, you can fix the dates by unlocking the payrun, make the change and finalise it again. Depending on your STP status for said payrun, you might also need to consider creating and lodging an update event so ATO would get notified about the change of dates. Here I found 2 articles from our community for your reference:

1. Can I unfinalise a payrun after its been finalised?
2. Create and lodge an update pay event

Please let me know if you have any questions or if I misunderstood your question.

Thank you,

Georgia