Despite the fact that the CERB has ended, the CRA is still accepting retroactive application until December 2, 2020. You can apply for the periods 5 to 7 through the CRA’s My Account or by calling the automated toll free numbers listed on the CRA website https://canada.ca/
But to apply for the periods 1 to 4 you should speak to a CRA agent on phone. More documents might be required before you can apply for these periods. To get more info about your eligibility to the CERB you can consult the CRA website or contact us on contact us directly.