Hi,
Generally both gastritis and GERD rarely occur together as the pathophysiology of both is different. While H Pylori is a causative pathogen for Gastritis, it decreases symptomatic GERD. So one needs to discuss the specific Symptoms that you have and treat them accordingly.
Anyhow, specifically for your question, significant reflux can be because of several reasons. It may be due to delayed gastric emptying in case of significantly inflammed antrum of stomach (causing pyloric spasm), due to weak lower esophageal sphincter, a hiatal hernia, supradiaphragmatic belch syndome and several other reasons. Patients with IBS also tend to have a lot of reflux and gastritis. In general, besides specific medical management, diatary management helps a lot in long term control in reflux symptoms.
First of all, any diet rich in fat, cocoa and too hot or cold liquids will precipitate both gastroparesis, pyloric spasm as well as reflux. High simple sugars are also detrimental, although indirectly. During the healing phase, large meals with a long gap between meals is also not very good for the healing of stomach. Dry fruits, while not very high in fat content, have larger residue, and take time for emptying out of stomach. Oats are fine, but avoid them at night. Avoid milk based diet while moderate amounts of curd based diet is useful. However, more importantly, diet restrictions should not be taken as a burden but as a routine.
Feel free to discuss more on phone if you like.
Best wishes for exam.
Next Steps
A detailed discussion is needed for dietary management. A detailed evaluation for etiology is important and should be done soon, probably soon after NEET exams.