Trainline: How to import a pdf eticket into the Trainline App?

My wife bought an eticket for me with her Trainline app for UK railways. The Trainline Help Page says

eticket

Open the email we send you with the PDF(s) attached – this is separate to your booking confirmation email
If you like, you can add the eticket(s) to our app or Apple Wallet

And elsewhere it says that the advantage of an eticket that comes by mail is that you can forward it to someone else. My wife has forwarded the mail to me and I can see the pdf eticket in my mail, but I’d like to have it in my Trainline App on my phone, logged into my Trainline account. The trainline help pages are maddeningly uninformative. Is there a way to do this, please?