6s upgrading to ios14 only

[mwi555]

My sister has a used iPhone 6s with ios12 currently running that we picked up from a family member. She needs it for a different family member for a medical device that will only work on iOS 13 or 14. We’d like to update it to 14 to have the latest software for the iPhone. When I try to download an update it only gives iOS15 as an option in settings, general, software update (ios 15 cannot work with the medical device and system).
How can I completely wipe this phone and install a fresh version of ios14 on it for my family member? Thanks for any advice.

 

[Jeqry]

I think Apple is still signing iOS 14.8 so google iOS 14.8 ipsw for 6s, download it, and restore from iTunes. Do this as soon as possible as Apple might stop signing it soon then it will be impossible.

 

[appltech]

Hi! There's a guide how to do the above mentioned, but i'd backup the iphone before that just in case. The file @Jeqry mentioned is located is on the ipsw web-site or there are alternative links in video description