Here's the safe way to do it. First, turn the printer completely off. Open the housing by pressing the snap latch and remove the label tape roll.
Next, take a soft cloth or a cotton swab and moisten it with a little ethanol alcohol. Gently wipe the print head—it's a precision part, so don't scratch it. Let the alcohol evaporate and the head dry completely before you put a new tape roll in and close the housing. Only then should you turn the printer back on.