Added bank account balance in journal (trader before) but when reconcile bank account the balance starts with 0. How do I change starting balance?

You'll have to change the starting balance in the account's register through the Chart of Accounts page, @Justyna2. This way, you can start reconciling and make sure your account matches your real-life bank transactions.

Based on your description of the issue above, it seems that you're reconciling your bank account for the first time after adding its balance through the journal. To fix this, here's how:

1. Go to the Gear icon. 
2. Select Chart of accounts.
3. Locate the account, then go to the Action column and select View register.
4. Search for the opening balance entry. It should have “Opening Balance Equity” in the Account column.
5. Select the opening balance entry to expand the view.
6. In the Deposit column, edit the balance so it matches your bank records.
7. Click Save. 

I've attached a screenshot below that shows the last three steps.

To learn more about this process, you can check out this article: Fix beginning balance issues during your first reconciliation in QuickBooks Online.

After changing the starting balance, you can reconcile the account again. For the step-by-step guide, kindly refer to this article: Reconcile an account in QuickBooks Online. It also includes instructions in editing completed reconciliations.

Once done, QBO automatically generates a reconciliation report. This way, you'll have a reference in making sure your books are accurate. In case you want to view, print, or export one, you can refer to this article for the complete details: How do I view, print, or export a reconciliation report?.

Please let me know if you have other concerns. I'm just around to help. Take care always.

Thank you! I added the bank balance in journal previously so I only had to add R by the transaction and all looks good now.