ender 3 neo hotend replacement

hi all,
1st time here and hoping for some help.
my hot end over extruded and snapped all the wires in the hot end. I replaced with a new hot end and I’m pretty sure I replaced everything as it was but when i turn machine on now on the screen at nozzle picture the top figure gives a temp and the bottom temp shows err under the hot end picture.
do i need to do something with software after change or have i screwed it up?
printer is only a few months old but i’d rather sort it myself if i can rather than going down the warranty rabbit hole.
any help appreciated thanks