I suggest to flash the GPU vbios again by spi programmer.. don’t use Nvflash
Perhaps this method could solve the problem, but I recommend choosing the VBIOS from a device with the same ID as yours.
https://www.techpowerup.com/vgabios/281769/281769
With modded Bios - Before put the 1070 mxm gpu You must to choose an SG mode into bios then save the settings then turn off the laptop then put the 1070 gpu into the master mxm slot