Perhaps if your LO doesn't nap in the afternoon, you let him play all day till bed time get a warm shower then make him sleep. That's what ill do to my first daughter, 5 years old. She goes to KN and once home she's not asleep, we will let her tire herself till bed time.
try to stop screen time at 2 or 1 hour before sleep the least. try to dim the light and put some essential oil diffuser..it helps