Use "Madam Chair" or "Madam Chairman" to address a female chair. The term "chairwoman" can be used if there is a particular reason to make the clear distinction that a female is fulfilling the role.

Is it correct to say chairlady?

A chairman is the leader of a business meeting or group. ... The noun chairman can refer to this person, whether male or female, though sometimes a woman is called a chairwoman. These days, it's more common still to simply call her (or him) a chair.

What is correct chairman or chairperson?

The Oxford Dictionary of American Usage and Style (2000) suggested that the gender-neutral forms were gaining ground; it advocated chair for both men and women. The Telegraph style guide bans the use of chair and chairperson; the newspaper's position, as of 2018, is that "chairman is correct English".