Do you have lavender plants where you can get the flowers from? I cut mine each fall and hang them upside down to dry. Or you can get dried lavender flowers on Amazon. Then I fill little organza bags with them - and add some lavender essential oil to increase the scent.
I make a simmering pot using lavender. It smells so good and freshens my entire house.
Pour the lightly crushed flowers into a large bowl or plastic bag. Add 1/4 cup of orris root per 4 cups of lavender, or 1-2 tablespoons per 1 cup of the potpourri mix. Orris root, which has little scent of its own, will help preserve the flower and herb fragrance.
This article may help: https://www.doityourself.com/stry/how-to-make-lavender-potpourri