I have done MD simulations for aqueous electrolytes in LAMMPS but I am not able to start with Ionic liquids, can anyone give me any idea how to start?
Ionic liquids are quite complex and I am not able to process how should I apply force field parameters to the simulations,
That is not really a LAMMPS problem. You need to find yourself a tutor/adviser/collaborator that has experience with such systems that will train you. An online forum is not very well suited for that purpose.
Failing to find a tutor, you would have to try and infer how such systems are set up and parameters assigned from the published literature. Good papers have a models and methods section with the relevant details.