How can I rid the room of past smoke?

Don’t forget the ceiling with the barrier paints. And look at having the floor sanded and refinished, too, and don’t forget the closet space and adjacent rooms for all of the above. Clean the HVAC vents and returns — dust and lint and smoke residue will linger there. There are also products sold in auto parts stores for removing odors, so try that.

Everything needs to be washed from ceiling to floor. Were the walls walls washed with TSP prior to painting? If not, you are looking at replacing the drywall as this important step was skipped. One must always wash walls before painting, no matter how clean you think they are. Closets cleaned and painted. Don't forget the ceiling. Wash, prime and paint. Curtains or drapes need to be washed or sent to dry cleaner. If there is carpet, it needs to be professionally cleaned. Any clothes in closet will have to be washed and quarantined until the closet is ready.

My father used to run a turn key service and swears by ozone generators for homes permeated with smoke odors, even after cleaning and painting. You set it in front of a box fan and let it run for 30 minutes on a timer. You can't have people or pets in the home while you run it or 30 minutes afterwards.

This is the one he used and it comes with the timer: https://www.foreverozone.com/collections/air-ozone-generators-for-odors-mold-green-pest-control/products/3500-mg-h-bare-bones-ozone-generator

He gave one to me after he retired and I used it for a car someone smoked in. It did an amazing job of clearing the smell out.