Divorcing from wife and we have been physically separated for over a year but she filed as head of household, how do I file

If you were still legally married in 2019 you file married filing separately.

Your separated spouse can file as HOH if she lived apart from you, and paid more than half the cost of keeping up her home, and provided care in her home for more than half the nights of the year to a qualifying person who is usually a child dependent.

If you also meet those qualifications (specifically, you provided care in your home for a different child dependent more than half the nights of the year) then you could also file as HOH.  If not, you file as "married filing separately."

Alright thank you for the help