What @kyrareh said!
First, recognize that it’s not a character flaw or disrespect and your child isn’t “choosing” it. Then, work on time management skills, which are lacking due to ADHD.
This webinar on time blindness with Ari Tuckman is packed full of tips and strategies:
ADDitude Community Moderator, Author & Mentor on Parenting ADHD, Mom to teen w/ ADHD, LDs, and autism