my obc ncl rank in jee mains 2017 is 140797 and i am not eligible for jee advance . so with the abive rank can i get any govt college if yes the how will it be done , externally or by josaa???

Since you didn't state your category, state, I would like to answer this in general category perspective.

If you're from any North Eastern state, then you have very good chances. ReadKhaja Hussain's answer to What is the last rank in JEE Mains to get admission into a NIT?

If not, then let me clarify something first—you won't get anything substantial with this rank in JOSSA.

With this JEE MAIN rank, you'll get preference in private universities/colleges in Chennai and Bangalore. You can easily get into a number of local colleges, but that's may not be a good idea.

So the choices you have now are:—

Concentrate on State level entrance examinations and score well.
Join any good private University or colleges from state level/any other entrance examination like VITEEE, BITSAT…
If you have a strong desire to get into IIT/Nit, drop out. Join any good coaching institute.