Pull out the smaller circle lid ;)

Unscrew the grey wheel at the bottom of the grinder in an anti-clockwise direction. (also used to adjust the grinding thickness) Then you can remove the central part of the grinder. Attention! It still has a spring above the centre rod. The thinner end must be towards the inside of the grinder. Filling. Reassemble the parts. Note: if the wheel jams when unscrewing: turn the grinder upside down and briefly turn the rotating part back and forth=> jammed grains fall inside. And when adjusting the grinding thickness, you have to press and turn the grey screw. Takes some force.
Only the old models with metal grinders can be filled from above.

I have the salt mill and you can just pull out the chrome steel plug at the top to fill in the salt, very easy.