Reflux : is usually causes by a weak valve at the end of the esophagus as it enters the stomach so the stomach acid goes backwards up the esophagus and causes pain. is there any solution to fixing the weak valve ?

There is no valve. There is a fold in the tube with muscles that draw it closed like a purse string. Things like caffeine/nicotine make closure weaker, laying down after feeds places extra pressure on the entrance. The stomach has muscular actions to churn/mix the foods with acid before entering the intestines. This squeezing can push acids against the entrance. Everyone can have reflux.