Is it safe to bake in an oven with melted plastic residue left?
My suggestion would be to let it run at its highest temperature setting for a while (if it has a pyrolysis/heat-cleaning setting, you can also use that). Best open some windows to let the fumes escape.

When it doesn't smell and smoke any more, I would personally consider it safe to use again, especially at lower temperatures than the one you used to make it usable again.