We transitioned to Mama-assisted to Liebling alone sleep at about 3.5, as he wouldn't sleep with me there. I did it with coffee.

After cream, medicine, story and prayers I would turn off the light and say "Mama is just going to have a coffee, I'll be back when I've finished."

I would go back when he called out, drink in hand, to show it was a real reason.

He put himself to sleep within 10 mins 9 nights out of 10. Rarely awake after my coffee.

Depending on the child, this may work earlier for you.