What is the ruling of Islamic law regarding a man marrying a woman who has previously committed zina and concealed it from him, and what should be done if the man discovers this in the future?

A woman must sincerely repent of the sin. The hymen repair surgery is not permissible unless the woman fears for her life or exposure to severe harm. Her marriage is valid, and she is not obliged to inform her husband; rather, she must conceal her secret and repent to Allah.