How do I activate new Koodo SIM card to existing account?

That sim was an inactive SIM, you willl have to switch SIM card in selfserve first before using it.
By the way, is your Koodo still active? Did you set your account into seasonal hold?

I did not set account to seasonal hold (I didn’t realise that was an option!), so my Koodo account is still active. How do I switch SIM card in self-serve?? I looked all through it and couldn’t find how to!! 

You could follow the instructions on this link to switch sim card https://www.koodomobile.com/en/help/koodo-sim-support 

I had already looked at that link. None of the support links help. It should be simple to go to my account and indicate the new SIM card number that applies to my existing phone number attached to my account, but I cannot find anywhere to be able to do that… I’m not trying to “switch” SIM cards (that requires access to the old card - if I had my old card, I’d use it!!).
I cannot schedule a call back from customer service because they cannot phone me because the SIM card is not associated with my phone number. I cannot phone 611 to get to customer service because the SIM card is not registered on the Koodo network even though the phone recognizes it as a Koodo SIM card.

I’m a little annoyed because the whole reason I chose the Samsung 23 Ultra from Koodo for my upgrade was that it said that it had dual (physical SIM cards) and I liked the idea of being able to add a second SIM card while travelling. When I received my phone, I found that it only had one SIM card slot but supported a second eSIM. Thus, when travelling and purchasing a physical local SIM I had to remove my Canadian SIM card, allowing it get misplaced during the 2 months I was travelling. Until I can match up SIM card to my account I have a wifi only brick, but no phone!!

Have you looked into the detail of the link. I took a snapshot of it below 

As I said I don’t have the original SIM card (otherwise i’d use it!) so I would be unable to recieve a verification code if sent to my LOST SIM card!! That is exactly the problem I’m trying to solve. I have a replacement Koodo SIM card that has never been activated/registered…. but need to be able to do so without the old card.

In the text from the link above, it said Koodo system can send a verification code to your Koodo email address. That was why I posted it there.

If you are overseas, you could as well and seek assistance via Facebook/X messaging and see if they help you. Links are below at the bottom of this forum

Thank you Dinh. My phone is now working with my new SIM card.
I had seen the page you copied but couldn’t get past the info at the top in bold that referred to keeping the old SIM in the phone to receive a verification code! Consequently, I had overlooked the possibility of getting the verification by email… Thanks for your help, as I’m not sure I’d have ever found the email verification option without your persistence.