Hi,
You can do it by following below steps,
Go to transaction QA32 and after UD you go to Inspection stock posting Tab as shown in below screen,
On above screen click on tab 
.
Now you will get the posting date option as shown in below screen,
Here you can enter desirable posting date e.g. for previous period also if period is still open.
Afterwards, enter and save the transaction. In this way you can post UD in previous period or desirable date.
Regards,
Narresh