How to Recover Lost Data in QuickBooks
I might have deleted some entries that change the numbers in the balance sheet.
How could I use the backup file to get the previous numbers without overwriting and duplication the existing data?
Before you think about accessing your backup file to recover the "lost" data, run your Audit Trail
report. It is found under Reports> Accountant.
The report tracks changes to entries. You should be able to find the transactions you deleted with all the relevant details you need to reenter them. This will save you having to go the backup file recovery route.
To help prevent this type of error in the future, make sure your set your closing date to prevent changes to closed or reconciled periods.
Let me know if this works for you. If not, I'll explain the backup datafile recovery route.