It's nice to see you here in the Community, Jaime.
Let me help and provide information on how to change your deposit category in QuickBooks Online (QBO).
If you just want to change your category from Mobile Deposit to Per Diem and not amount, bank account, or date. You don't have to open a closed bank reconciliation.
To change your category, you just have to open the register holding the transactions, and then make the necessary changes to correct the category.
For future reference, you can check these articles to guide you in running a report and what to do if QBO doesn't match your bank statement at the end of a reconciliation.
Please don't hesitate to leave a comment below If you have any other concerns about correcting a category. I will answer them in any possible way.