Answer:
place it in a magnetic field
Step-by-step explanation
Ferromagnetic materials are made up of small domains which are randomly oriented in it. Due to this random orientation of all domains they do not produce any magnetic field in its surrounding.
When we put ferromagnetic substance in external magnetic field then due to this all small domains in ferromagnetic substance will experience torque and try to align in the direction of external magnetic field.
Due to this alignment of all domains it produce it's own magnetic field in the direction of external magnetic field.
This phenomenon is known as magnetization.
So here correct answer would be
place it in a magnetic field