Accidentally added a deposit that I put in manually the day before

Deleting an account in the Chart of Accounts isn't possible in QuickBooks Online (QBO), LM424. 

Firstly, please know that QuickBooks Online relies on the downloaded bank data from bank institutions. Since the transactions appeared as payments, it's recommended to exclude them from your books.

Also, when you deactivate an account, the entries associated with it will not be removed. Instead, they'll stay connected.

When you inactive an account with a balance, the program will make a journal entry to move the remaining balance to another account. The existing transactions won't disappear and will still be linked to your financial reports.

Further, the option to delete inactive accounts is unavailable. If you want to erase it from your books, consider merging them to another account.

Since the account you want to delete is inactivated, you'll have to reactivate it first and then merge it with another account to remove this from QBO permanently. I'll gladly walk you through it.

1. Go to the Gear icon, then select Chart of Accounts. 
2. Beside the printer icon, click the Settings icon. 
3. Under Other, tick the Include inactive checkbox.
4. Locate the account, then select Make active.

1. Find the duplicate account you don't want to keep. Then, click the dropdown in the Action column, then Edit.
2. Modify the Account name (Name), and Tax form section (Detail Type) so the duplicate account's detail matches the account you want to keep. 
3.  If you're ready, choose Save, and then click Yes, merge accounts.

Furthermore, it's best to seek your accountant's advice if you're planning on inactivating an account in QBO for guidance.

For reference, please read this article: Make an account inactive on your chart of accounts in QuickBooks Online.

I'll also add this article for future reference if you want a detailed step on reconciling an account in QBO: Reconcile an account in QuickBooks Online.

I'm more than happy to assist you if you have further questions about deleting a deleted account in QBO. Just click the reply button.