When the nlread() function read a car file, it will return a molecular configuration. You can know the elements, and the cartesian_coordinates. In order to convert this configuration into a bulk configuration, you have to define the bravais lattice by yourself.
your_molecule = nlread('yourfile.car')[0]
your_lattice =.....
bulk_configuration = BulkConfiguration(
bravais_lattice=your_lattice,
elements=your_molecule.elements(),
cartesian_coordinates=your_molecule.cartesianCoordinates()
)