You may want to return or repay the CERB if you:
return to work earlier than expected
applied for CERB but later realize you’re not eligible
To return or repay your CERB payment:
If you still have the original CERB cheque, you can return the cheque by mail to the address below.
If you don't have the cheque or were paid by direct deposit, you can mail your repayment to the CRA. Be sure to:
make the payment out to “Receiver General for Canada”;
indicate it is for “Repayment of CERB”; and
include your Social Insurance Number (SIN) or your Temporary Tax Number (TTN).
Mail your payment to:
Revenue Processing – Repayment of CERB
Sudbury Tax Centre
1050 Notre Dame Avenue
Sudbury ON P3A 0C1
Source: https://www.canada.ca/en/revenue-agency/services/benefits/apply-for-cerb-with-cra.html See the bottom of the page.