How to update topology file after insert-molecules?

I think I got the solution.

Add
#include "ligand.itp"
under
#include "amber14sb.ff/forcefield.itp"

Add
#include "ligand.top"
before
#include "amber14sb.ff/tip3p.itp"

Add
ligand 26
to the last line

Then, in the ligand.top, disable the sections of [defaults], #include "ligand.itp", [molecules]