I'll ensure you'll be able to enter your December-21 until March-22 figure in QuickBooks Online.
Depending on your preference, there are plenty of options to enter those data. You can create a sales receipt or invoice if it's money in a transaction. Then, record it as a cheque, expense, or bill for money-out transactions.
Option 1: Create a sales receipt for money in a transaction.
Click the + New icon.
Select Sales receipt.
Choose the customer from the Customer dropdown. If you haven't set them up hit Add a new customer.
Fill in the sales info, such as the payment method and the date.
For future reference, I've added this resource about reconciliation to ensure your QuickBooks balance matches your bank or credit card balance: Reconcile an account in QuickBooks Online.
If you have additional questions about recording transactions, leave a message in the comment section. I'll be happier to help. Have a nice day!