Run the simulation using the last checkpoint file i.e., md_10.cpt in same directory.

You can try following commands for 200ns:

gmx mdrun md_10 -cpi md_10.cpt -nsteps 100000000 -apend #(no. of nsteps required to reach 200ns time scale)

You can use the commands in a sequential manner,

$ gmx convert-tpr -s md_10.tpr -extend 190000 (time for further simulation in ps) -o md_200.tpr

$ gmx mdrun -s md_200.tpr -cpi state.cpt -noappend

It will start after the 10ns.

Further, you can concatenate all trajectories together.