The regular Static Meshes cannot be deformed in real-time, because they are hyper-optimized by the renderer, sometimes in ways that don’t preserve the original index/vertex relationship.
The Skinned Meshes can be deformed, but only by pre-declared morph targets, or by moving bones around.
To update actual vertex/triangle data in real time (possibly every frame,) you’ll want to enable the Procedural Mesh plugin in the Plugins list, and then use the API provided by that module (mainly, CreateMeshSection and friends.)
You could also look at the Voxel Terrain plugin in the marketplace – if you purchase the full thing, I think it comes with source code for the plugin, and you can read through it for ideas about how to do procedural geometry update.