I haven't had SA approval or medical request yet and I'm from the UK (the PA). I will insert just a section of the letter as it was quite long:
"You need to take this letter with you and go in person to any biometric collection service point to have your fingerprints and photograph taken. • If you are outside Canada or the United States, you may go to any Visa Application Centre (VAC) most convenient to you."
They did mention that you can't do it at a Canadian airport (only students and workers are able to do that upon arrival). Also just a note, we paid for biometrics with the initial PR fee so if you didn't do that I imagine you get a payment request first
edit: There is only one VAC in the UK which is in London, according to the IRCC website.