QuickBooks Online (QBO) is a read only-app. If you've connected your bank account, it will bring in transactions based on the data posted into your bank. To isolate the issue as to why the transactions came over as credits, I suggest checking your bank statement and compare the transactions posted into your QBO account.
However, if you've manually upload your data into the system, there's a certain format to follow. You can use either a 3-column or 4-column format. Here's a great resource that you can check for guidance: Import bank transactions using Excel CSV files.
To correct the imported transaction, you'll need to exclude all transactions and delete to start over. Once done, prepare your CSV file and be ready for upload.
To upload, here's what you'll need to do:
Go to the Banking menu.
Select the Banking tab.
Choose the blue tile for the account you want to upload the transactions into.
Pick the small arrow ▼ icon by the Update button.
Hit File upload and follow the onscreen instructions.