Hi, I'm on the part of the tax return about changing the direct deposit details. Last year I did my tax with taxback, will the CRA have my bank details?

If you are not able to get into CRA My Account, then there are other ways that you can check/change your direct deposit information. This CRA page has a list: https://www.canada.ca/en/revenue-agency/services/about-canada-revenue-agency-cra/direct-deposit.html

If you are going to mail in your return, then you can include a copy of the direct deposit form with your tax return. You can download the form here: https://www.tpsgc-pwgsc.gc.ca/recgen/form/inscription-enrolment-eng.html