The first step in treating IMO is normally getting your bowel opening once a day. Allowing a comfortable passage of food through your gut helps to reduce bloating, and gas caused by blockages. This may need laxatives, fibre, physical therapy, more movement or a combination of these approaches.
Getting rid of high methane gas production depends on the cause of your intestinal methanogen overgrowth. For example, if your slow transit time and constipation was caused by undereating, or a low fibre diet then we need to look at long term diet strategies. If your IMO was caused by an adhesion or structural blockage a diet change may not make that much difference.