Here is the solution:
First we need to find our grub config file. We can do it using:
We should get something like:
> search.file /boot/grub2/grub.cfg
Now load that config:
The grub menu should appear. Unfortunately entries were incorrect because of using e.g. "linux" command instead of "linuxefi". We have to change that, so press "e" to edit your entry. Next, change "linux" to "linuxefi" and "initrd" to "initrdefi".
> configfile (hd1,gpt6)/boot/grub2/grub.cfg
To boot press F10.
After your OS is loaded open YaST, then go to Bootloader settings and change mode to "GRUB2 EFI". Done!