I think your talking about Marsilea quadrifolia. If this is the case, just cut a few inches off the top. You don't replant these. However, this plant is much like hair grass and their can be a die back.
So that is pogostemon quadrifolus, often referred to incorrectly as Pogostemon ‘Octopus’ (again it is misapplied).
To trim you can cut it wherever you like, and for sure replant the top! It rebounds immediately