Simple Re-save .stl files to .step $35

Hello we need to convert all of our 3d files into .step format. Some of the files have 2 different versions within the file. For example our mech miniature files have a connected and disconnected version SEE EXAMPLE. We only need to save the connected version. There are the following files: 7 Mech files 3 Weapon Group Files 1 Truck 1 Building 1 Turret 1 Drone 1 Giant Robot = 15 files. Just the 7 Mech files have the different versions like in the example image.