Great to see you in the Community, @Lhorie27. Yes, you can reconcile the data from the bank via .csv file in QuickBooks Online (QBO).

You may want to upload the c.sv file first to the correct bank account that you want to reconcile. I'd be happy to guide you through the steps. 

Here's how:

1. Go to the Banking menu and select the drop-down icon beside the Link account button.
2. Select Upload from file and locate the csv file that was given by your client.
3. Click the Continue button and map the data in the file correctly.
4. Follow the on-screen instructions and select Done.

This is what it looks like:

Once done importing, you can now proceed to the reconciling process. I've got an article that contains the steps on how to reconcile: Reconcile an account in QuickBooks Online.

Please feel free to get back to me here for any additional questions about the reconciliation process. I've got your back. Take care!