I experienced IBS symptoms for about a week then I jumped on a 13 day water fast to lose weight. I noticed that when I got back to eating food again that my IBS was gone. So yeah fasting has definitely helped me.
Get a decent enterosorbent and use it 7 days prior to your fast. Do OMAD for the preparation week with breakfast of a simple breakfast - buckwheat porridge cooked in water and nothing else. Shouldn’t have any IBS with the buckwheat, the sorbent will cleanse your GI pretty well heading into the fast. Do the same for a week coming out. Treat it like a 3 weeks course of medication. It will be boring af but you’ll have no issues following provided you get a good dry fast in-between