Is it permissible to use a work device to print private study materials, and what is incumbent upon one who has done so previously?

It is not permissible to use work tools for personal gain unless explicitly or customarily permitted by the employer. As for what you did previously, you should seek permission from the authorized officials, and if they do not permit it, then you must pay compensation for what you used, based on the saying: "On the hand is what it took until it returns it."