A customer deposit was deleted by mistake. How do I manually add it back in to QB.

I’ve got your back in manually entering a deposit in QuickBooks Online, @svp2. 

Beforehand, you’ll want to ensure if there's an associated payment on the invoice from your customer. If necessary, you can use an audit log to review your transactions. 

Then, if you haven’t already, put invoice payments into the Undeposited Funds account. This account holds everything before recording a deposit. 

From there, you can now record the bank deposit. I’ll show you how: 

1. Click + New, then select Bank Deposit.
2. From the Account dropdown, choose the account you want to put the money into.
3. Tick the checkbox for each transaction you want to combine.
4. Make sure the total of the selected transactions matches your deposit slip. Use your deposit slip as a reference.
5. Click Save and close or Save and new. 

For more details about entering deposits in QBO, feel free to check out this guide: Record and make bank deposits in QuickBooks Online. 

Furthermore, I’ve added these resources that may come in handy in organizing your transactions in QBO: 

• Categorize and match online bank transactions in QuickBooks Online
• Reconcile an account in QuickBooks Online

Please let me know if you need clarification about bank deposits in QBO, or if there's anything else I can do for you. I'll be standing by for your response. Have a great day, and stay safe.