Ming from Agents of Speech explains how to build toward speech through oral motor exercises. Every exercise must connect to a specific sound goal, and you practice the target sound right after the motor work. To teach /l/ when a child can't lift their tongue, start with side-to-side movements, gradually angle the tongue up, then try the sound.
The most basic thing you have to understand as a parent, from the motor to the speech transition is something that is very difficult for some children. It's nearly impossible in the beginning. So that's why oral motor tasks have their place in therapy. But for every oral motor task, we must have a speech goal in mind, or else you're just really teaching them how to just do the oral test. So we must practice the sounds right after we do the oral motor exercise. There's no point in just doing it. And of course, there are some prerequisites towards oral motor actions, like oral motor movements. For instance, I was talking about the L sound like the tongue needs to go up. But what if the child cannot do the tongue going up? Then we need oral motor exercise that bridges the tongue to go up. So we're not going to do the sound because we haven't even hit that place. So what we can do is the tongue left and right, and then slowly move the tongue up diagonally until you hit the top. And then after that, when the tongue is at the right place. And then you can try with the speech sound. So you see, it's a stepping stone.
