How do I correct an error I made in tax deducted at source? I have not fidedmit yet.

If you have not yet filed, you can edit any item on your on-line return.
If your tax deducted is on a T-slip, open the Income tab and select T-slips.
Find the T-slip you need and enter the correct tax deducted, using the slip.

Thank you. That was simple.