If you wish to get into another college through JOSAA counselling then you have to cancel the admission you have applied through TNEA counselling. By this process you may not get all the money in refund from the college of TNEA but yeah! you can do it. And for the admission through JOSAA you need to have a Cancellation certificate from the college and you may have to submit that in your college through JOSAA.

To know more about JOSAA counselling visit the link below:

https://engineering.careers360.com/articles/josaa-counselling

To know more about TNEA counselling visit the link below:

https://engineering.careers360.com/articles/tnea

I hope this answer helps. All the very best for your future endeavors!