Ditto food diary, write down what you ate and try to correlate to your symptoms the next morning (i.e., every night I eat a spicy curry/chili my next morning is hellacious ). Unfortunately there's no one-size-fits-all approach to treating an UC. Very, very individualized especially when you're talking diets and supplements. What's one's miracle treatment for UC does absolutely nothing for another, and even makes another's symptoms a whole lot worse. So, realistically, what you have is a large toolbox of things to try and lots of time to try out the tools you feel might work best. Knowing it is all trial-an-error, with no guarantee of any single treatment working for you. Sorry but there's no easy-button for this.
I have not found a single supplement or diet to help my UC symptoms, despite trying many over the years. Most have very little scientific evidence, if any, behind their effectiveness. Doesn't mean they cannot work, some ancedotal evidence they can help a little. The best evidence based info on diets is this:
https://www.dietvsdisease.org/ulcerative-colitis-diet/Certainly, I would recommend sticking to the mild, anti-inflammatory mesalamine medications prescribed by your doctor (asacol, lialda/mezavant, pentasa, apriso, etc.) as they are well tolerated by most without side effects. And those do have sufficient evidence of their effectiveness in treating an UC. No harm in experimenting in diets and supplements in addition to said medications.