Software for updating iPhone to old version?

I need to restore a bricked iphone stuck in a boot loop.

I get an error when I do it through iTunes and have read it is because it is too high a leap from an early IOS to the latest IOS11.

I can download older versions of IOS but iTunes doesn't allow me to install them.

Does anyone know of any software that will allow me to do this?

I've tried iTunes, reiboot, redsnow, iCarefone, i4tools (Chinese software which is supposed to do it but I can't work out how to use it)

Can't downgrade to certain software because Apple doesn't sign them anymore - Unless you have blobs saved its impossible