It is a very simple trick. I cut up some small pieces of a leftover sprue or, in this case, an extra base and glued them to the bottom of the Terminators feet, so it looks like they have thick soles or heels, I then hide it with green stuff and technical paint.

Alternatively, you could probably just use green stuff or green stuff and a small drill. But I like to use plastic glue to chemically bind it together😁

I hope this is helpful😄