Anti-inflammatory foods are a good choice: https://www.nutriliving.com/blog/top-10-anti-inflammatory-foods
In addition, cutting out foods that may irritate: dairy, gluten, rough fibrous foods during a flare-up.
Drink plenty of water if you are experiencing diarrhea in order to prevent dehydration.
Avoid caffeine and artificial sugars.
Here's a previous answer to a Q about ulcerative colitis: https://www.nutriliving.com/nutrition-center/ask-an-rd/11205-can-you-suggest-nutribullet-recipes-ulcerative-colitis