Adding more fiber to your diet if you're constipated can be a very bad idea.

Adding fiber might help some people with constipation but this varies significantly from person to person. Fiber helps creates more bulk and thus helps push stools forward, easing constipation in some. For others, particularly those facing motility issues(the contracting muscular movements in the gut), adding fiber can cause more pain and discomfort. It's akin to sending more cars in the way of a traffic jam. For people with underlying gut issues, usually fiber is not well tolerated and worsens problems such as bloating, pain, constipation, diarrhea, and rectal bleeding. And reducing fiber intake eases gastrointestinal symptoms overall.

The idea that fiber helps constipation are based only on measuring stool volume output in relation to fiber intake, not taking into account actual symptoms and patient experience. You can experiment and see what works for you. People often find that reducing fiber intake while keeping caloric intake and electrolyte intake high often helps relief constipation.