Patta land now marked as dkt

An ex army person got assigned land which he sold after 12 years to X in 1991 After this X sold to Y and sold to Z in 1999 Recently it was reported that this land is marked as DKT. Z is in possession since 1999 I.e 21 years now. So can this be converted back to patta? Z has constructed a workshop on this land Can this land be taken back. Whom to approach to get this land marked as patta land again? This is in Madanapalle chittoor District Andhra Pradesh