How can I have my iPhone's iTunes version downgraded?

DorNabati wrote:

I bought myself two collectible devices and I am unable to return them to Itenus for restoration, I would love to hear solutions

If you can't update or restore your iPhone or iPod touch - Apple Support

If you have an older mac, try running iTunes on it. if not use a virtual machine and run a old version of iTunes such as 7, 8, or 10. You can also try downgrading iTunes from your computer, but many issues arise if you do downgrade.

Go to trusted websites that have older files