Assign frame numbers in a fake trr file

GROMACS version: 2018.4
GROMACS modification: No
Here post your question:

I conducted simulated annealing 30 times in a for-loop cycle and I want to analyze the final frames from the end of every cycle. I combined final 30 structures (.gro) into a single trajectory file. Currently, frame number for each structure is zero. Is there a way to assign frame numbers say 1 to 30? I need this to know these frame numbers in order to select most representative structure from the cluster analysis output. Shown below is my current output

Any insights on this?

Convert the .gro file to a binary trajectory format like .xtc or .trr and set times (even if they are not meaningful) with options in trjconv.