After registering for the "in-printiple" basis, you can still wait for the offer from the financial institution or lodge the complaint with FIDREC. In case, FIDREC rejects your complaint or offer an inadequate sum, you can proceed with the class action.
You must register now. If you wait until a later date, you may miss the boat. I will not be able to help you at the last minute. The contact persons are found here.