Tracking notification preferences for labels bought through eBay

My wife has been receiving tracking notifications by SMS on her phone for items I have posted using Australia Post labels I have bought on eBay. I only want these notifications sent to my email address. How do I remove her mobile number from my notification prefefences?

I foolowed the instructions in your link, however the IM option did not appear. I was told that my delivery method was by email, no mention of SMS.