How to legalize encroached land

My father purchased a plot In 1985 in a town in Karnataka it was then a town municipality in our area now it is changed to city municipality corporation North end of our house face the street/lane it's not a main road it's a small connection road in residential locality But the southern part of is dead end after our land there is a government schools boundary there is a piece of land 13feet/40feet which we have encroached and construction was done 20years back as no one object to this because it was a government land and a dead end no one else can use this land now I want to legalize that land what are options available for me I can pay the fine or anything and legalize that in municipality or I have to approach court I have heard that ulc law is there can it help me