Unlocking phone carrier on iPhone 11 without iTunes

I am trying to unlock my iPhone 11 from my mobile phone carrier. I requested an unlock from the carrier, who contacted me the next day to say that this had been carried out, but would not be completed until I connected my phone to iTunes. I went to my MacBook to do this, and found that on my the current Apple software (MacOS Catalina 10.15.5) that iTunes no longer exists in the same form as it once did. But I was prompted to use Finder to connect the phone, and then followed the instructions to unlock the phone at https://support.apple.com/en-nz/HT201328- i.e. I first did a backup, then a factory reset, then restored the phone.

Unfortunately that has not unlocked the phone. I spoke to my carrier again and their only advice was that I need to connect the phone to iTunes- which as described I clearly can't do. How can I go about unlocking the phone successfully?

Thanks