The system updates the bank transaction list automatically. Though, you can also do a manual update if you don't receive any updates.
In the Banking page, click the Update button.
Enter your Multi-Factor Authentication (MFA) credentials.
Click Continue update.
If you need more than 90-days worth of bank transactions, you can ask a valid WebConnect file from your bank. Then, import the file to QuickBooks Online. Feel free to browse these articles on how to import the file: