Another command from the basic group.
When a dog has already mastered sit and executes it well, we are in front of him and guide him with delicacy so that it lays down. Down and slightly forward. Let us react to dog movements and direct that his elbows touch the ground.
Then we praise and give a delicacy (when he is down). While rewarding repeat the command "Down" to better associate the word with an appropriate position. After a few repetitions the dog will understand that the movement of the hand down means it has to lie down, then it will have reward. Gradually introduce a verbal command, for example. down, lie down, square, etc. without eliminating the optical commands (guiding by hand). Every time we reward the dog with delicacy.
Over time, we eliminate the movement of the hand.