This is the Expert position. You know what needs to be done. You know what is wrong. You understand. You can give advice. And the person with dementia doesn’t know nor understand or is not seeing the risk that you see.
There are times the Expert position is necessary such as when physical safety is at risk. The person with dementia turns to walk into traffic with no awareness of the possibility of being injured. You can see the risk and they don’t. The responsibility for acting is with you to prevent them being injured.
This is also the position of advice giving. You have knowledge and can share it. They may not have knowledge for the situation. You know the plan for the day is to go to lunch at the golf club and requires a rather formal standard of dress. You can suggest or tell (perhaps) the person what to wear. “You’ll need to wear a tie. That green one looks good on you”. This is the Expert position.
Tomorrow is the Columbo position