no diet or exercise is going to help. use the betamethasone cream and manual stretching but be careful. do not keep the foreskin forcibly retracted or you may create a painful condition called paraphimosis. i do not know you age but your glans should be fully retractable in your early teen years or before unless you have some adhesions (tissue still attached). without an exam i cannot comment. rather than treat yourself a consultation with a good urologist now may be beneficial to you.
suggest any medicament or excercise for curing phimosis. any diet for such. i regularly do gym and drink 3 litrs water. i have done survey on internet that phimosis can cured using betamethasone topical cream. i have done penis stretching and used betamethasone cream. my phimosis is now suppressed. but when my penis errect it doesn't show my glance penis out of skin i have to stretch manually.