I too see that the option to 'add item' from within the incident ticket is not available. What I currently do is 'Merge' the ticket with an already created SR. In your case, you would simply create the SR for 'new laptop' and then merge the two. If there's another way to do this I'm all ears!
As a feature request, I would like to see this added as an option. When viewing, for instance an 'Incident' ticket, the 'Associate' menu in the upper right corner should have an option for 'Service Request' as well. There's options for Problems, Changes and Projects, but not Service Requests?

Hi all,
I will forward this case to our product team and see if we can get this enhanced in our future deployments.
We also recommend converting the Incident to a Service Request for the replacement request that you receive.
Please let us know if this isn’t helpful.
Happy supporting!