Hello Palalala,
Have you had a chance to view the SIM card from your existing phone? As far as I am aware, Fido has been using Tri-SIMs or multi-sized SIMs for a while now (see image here). If your existing phone uses that type of SIM, you might be able to simply remove the portion, altering it to the proper nano size.
On the other hand, if your existing SIM card is of the single-sized type, you would need to update the SIM card. Unfortunately, I don't think it is possible to update the SIM card for a pre-paid account online. As far as I am aware, it needs to be done in-store (see here).
That said, Fido has upgraded its Manage SIM Card option for post-paid account users (via My Account). I'm not sure whether Fido has re-instated access to My Account for pre-paid accounts. You should note this forum is community-driven and not intended as a venue for customer services. If you would like to verify whether pre-paid accounts have access to My Account, you would need to contact customer service. If not, they might be able to update the SIM card information for you. While they can also be contacted via Facebook, or Twitter, you would likely need to contact their dedicated pre-paid accounts line.
Hope this helps 😀
Cheers
