Ender 3, ender extender (400x400 build plate), 4.2.7, CR Touch

Can’t set Z offset as shown in videos. Auto home zeroes X & Y, Z 25-30?, then moves to x=~270, z=~220, z~40. Unable to set z to anything near ‘0’.

I have the same kit, and apparently there are some problems with it. I have a creality 4.2.2 board in it, and there is marlin firmware 2.0 I think. The person I bought it from says that he cannot get it to build any larger than the original footprint.