How can I go back and check my T4 inputs? Obviously there is a mistake somewhere as the tax refund calculated is absurd; $240,000.00 absurd.

That would a very sweet refund!!

If you are using TurboTax Online, click on Income tab => T-slips => T4. Once there, it should show you all the T4s you have entered.

I have filed my income tax wrong I put 2020 in with my 2021 which brought my income up massively showing that I owe the government $22,000 I need to fix that