See below @KNOXERANOIS , for how to change your SIM card. (This is presuming you're not saying that you believe you may have been SIM hacked, in which case please read and follow this process - https://www.publicmobile.ca/en/on/get-help/articles/sim-swap-fraud)
Sign into your self-serve, choose "Change SIM card", follow directions to reach out to Moderator to place ticket to process the SIM card change.
This follows an update which just happened 3 days ago per SIM Swap Fraud Announcement on Community homepage:
*March 8, 2021 Update*
To protect our customers from SIM swap fraud, we have temporarily disabled all online SIM swaps through Self-serve. To change your SIM card, please submit a ticket here
