There is no option to get back the old opening balance after updating balance in BUSY. Therefore, before updating anything in the data, take a backup so that if any error occurs, you can restore the backup data again.
And
To carry forward the updated balance of previous year to the current year, follow the steps given below:-
Step 1 : Go to Prevoius Year from Change Financial Year
Step 2 : Run Update Master Balances from House-Keeping
Step 3 : Go to Administation, then Change Financial Year
Step 4 : Press Enter on Current Financial Year options
Step 5 : The Carry Balances window appears. Select the Yes option, then select the New & Changed Masters option.