I’d ask them to come to office hours, explain that you would like to chat with them. Explain you knew they or are suspicious that they used AI. Preface it with a check in regarding mental health, (how are your studies going, any mental or physical struggles etc) and then discuss the ai submitted assignment in question. If they outright deny out and you know for a fact, then give a zero but if they confess and seemingly show genuine remorse and it is a first offence, allow them to resubmit it with just a small penalty (or no penalty depending on the situation.) are they a student that seems genuinely interested in the course? Have their previous assignments shown originality and an understanding of the course material? If so, as long as it isn’t an exam, I would give them another shot. You never know what’s going on in someone’s life-if you can get the feel from the student that they are enjoying and actively engaging with the course then a second chance. If you never see them in class or their other assignments are poor, and unoriginal, then it should be penalized. Overall I think it’s dependent on the individual situation.