How can I take out the interest earned in my Super before rolling over to Hejaz?

You will not be able to determine how much interest or non-sharia compliant investment earnings have been generated during your time in a non-compliant Superfund.

It is not just the interest that is not sharia compliant but also returns and income generated from non-Sharia compliant investments within super. This makes it virtually impossible to determine the amount that you should omit from the fund.

Even if you were to determine this amount, you cannot remove this from your Super due to the Super regulations. You may just want to provide a certain amount to charity when you can access your Superfund in retirement, to ease your conscious.

Due to your good intentions, may Allah excuse and reward you for this thought. You do not have to worry too much about what has happened prior to you not knowing there were Islamic alternatives for Super. Now that you know, it is your duty to ensure your retirement fund is always Sharia Compliant moving forward.