How to add a tip mass to a cantilever beam in Finite Element Method?

I am trying to model a cantilever beam with a tip mass at the free end and trying to find its natural frequencies.

I have managed to find it for the cantilever without a tip mass. Now I have to somehow add the tip mass to global mass matrix but I dont know how.

This is the global mass matrix for 10 elements, having size of (20, 20)

How should I add the tip mass into this global mass matrix?

Thanks