Pls give me some recommendation about hw to prevent mouth smelling due to gastrite?

Treat the source: If the bad breath is caused by gastritis, or acid reflux, you should treat the gastritis with antacids or tums (calcium carbonate). It could also be caused by an infection either in your mouth or in your sinus passages. If it continues it might need to be treated

Most common: Most common cause of bad breath is infection of teeth, gums, tonsils, sinuses, etc. Please see a Dentist for evaluation. If your halitosis is caused by a gastric problem, such as GERD, you need to control the problem. Mouth wash, pills, gum, sprays, etc., will not cure your problem, only temporarily hide it. Best to treat the cause. If Dentist says cause is not Oral, see your Physician.