First back up your chats within the Whatsapp’s settings on your old phone.

Then make sure your sim is in the new phone.

Setup whatsapp and then restore your chat history.

If that doesnt work, let us know what error you are getting during this process.

Thanks. I have tried all this, but I am unable to open WhatsApp. At the initializing stage, it says 'unable to connect'

Has you moved your number from another carrier into Koodo recently? Is your cellular data working normally?

As well, can you disable whatsapp in the previous device and activate it in the new device?