What if the navel ring is going down in the navel piercing hole?

Well I am going to assume you have a navel gem or a bent barbell and the ball is sinking into the top hole of the piercing (this is because your question wasn't clear enough). That would be a sign that the piercing jewellery is too short for the piercing and you are going through some swelling.

You should get into your local body piercing studio and have the jewellery changed as soon as possible, left unresolved this can cause serious issues for your piercing. All piercings discharge during the initial stages of healing, this discharge matter needs to be washed away daily so the piercing can heal. If the matter is left and not cleaned away the piercing can swell and become infected.

Aftercare is a daily requirement and not an option, it needs to be done every day to maintain a health piercing. If the jewellery is too short it can block the entry and exit points of the piercing stopping the piercing discharge from draining and thus causing further complications to occur.