How do I enter a corporation tax rebate in quickbooks online?

Welcome to the Community, @reigategreen.

You can enter a corporation tax rebate as a deposit and post it to the income tax expense account. Let me guide you how.

1. Click the Plus (+) icon.
2. Select Bank Deposit.
3. Choose the appropriate bank account from the Account drop-down.
4. In the Add funds to this deposit section, select the customer from the Received From drop-down.
5. In the Account drop-down, choose the Income Tax expense account.
6. Enter the amount, then click Save and close.

I've got you an article for more details: Record and Make Bank Deposits in QuickBooks Online.

However, I still recommend checking with your accountant for more guidance. He/she may add suggestions based on what's more suitable for your business and to your books.

In case you need tips and related articles in the future, feel free to visit our QuickBooks Community help website for reference: QBO Self-help.  

Please don't hesitate to reach out to me if you have any other QuickBooks concerns. I'll be right here to help.