Turn off the baseboard heater. Let the heater cool down to room temperature. When the baseboard is cool, touch the plastic to see if the plastic has cooled. The plastic will harden close to the consistency before it melted.
Remove the baseboard heater panel that covers the electric coils. On most baseboard heaters, the panel easily lifts up and off the heater. Check the heater coils to ensure no plastic melted onto it. Baseboard heaters have a safety panel over the heater to avoid this and protection from possible burns.
If you cannot remove the baseboard heater panel, place a bag of frozen vegetables on the melted plastic for about three minutes to ensure the plastic hardens completely. Placing the frozen bag on the area can also pucker the plastic for easier removal.
Find an area of the melted plastic that is lifted or can easily be removed. Put the corner of the putty knife under an area of the melted plastic that is lifted. Gently lift the putty knife until all or a piece of the plastic lifts away from the baseboard heater. Continue to remove the plastic by carefully placing the putty knife under the plastic and lifting it.
Wipe the baseboard heater panel with a dampened, warm rag to ensure all the plastic is removed. Replace the baseboard heater panel on the heating panel unit.