Hi and welcome to Arturia forums.
There a a couple of ways to do this. I suggest you look in the manual section "3.5. Macro controls" and section "11. MODULATION ROUTINGS".
When you are in "11.1.1.2. The Mod source view", then you can click and then drag the sliders in the center strip to add an amount of modulation, when the cursor change to a double arrow symbol, when your mouse hoover over a slider.
When you are in "11.1.1.3. The Mod target view", then you can click and then drag a ring around the parameter to add an amount of modulation, when the cursor change to a double arrow symbol. The symbol shows, when the mouse is over the edge of an parameter. You don't move the parameter it self but a ring around it.
This is what you directly ask about in your example, as i understand you, if you mean you select M1 in the center strip.
You can find the manual through the "? Help" in the main menu at the top left corner of the application, where it say "PIGMENTS".