At puppy course they taught us to:
1. Start playing with a toy and practice “let go”
2. If your pup let’s go, keep toy up in the air and make your pup try to get it
3. Once all paws are on the ground, give praise and start playing again.
4. Repeat until your pup understands 4 paws on the ground means play you can add the command when paws are on the ground. Then praise.
Eventually they learn the command means 4 paws on the ground.
Although my 6 month old still can’t hold her excitement in the first 5 seconds and then quickly sits down

so still work in progress.