For all the special move type achievements like this one, I highly recommended you check out the tutorial at the start of the main menu and familiarize yourself with the button mechanics of NHL 21.
For 'Manual Sauce",
You have to be locked in as a skater. You can easily do this in most modes but I would recommend going into play now and setting it to rookie.
You position lock by clicking in the
when you see the player standing there. You can cycle through and the positions> C,LW,RW,LD,RD. I would go with a C.
In the game, keep blowing by the defenders and manually passing the puck across to your AI for one timers.
You got to be fairly spaced apart but keep saucing that pass over with
until the AI gets it in. Not too difficult on Rookie.