How do I connect old iPhones to Wi-Fi for iOS updates when Wi-Fi is blocking connection?

Hi - I have a bunch of old iPhones that I want to reset and wipe in order to recycle but unfortunately I need to connect to wifi to do so. Given the phones haven't had any operating system updates for some time I think it is stopping them connecting to my home wifi. Given I have to have an internet in order to do the updates I am caught in a bit of a loop. Any ideas or work arounds? Thanks.

[Re-Titled by Moderator]