Unfortunately, you cannot strip the paint or varnish off of a piece like this (without stripping the original wood finish). This is because of how plastic and wood are bound together in materials like these.
This is because wood is porous, which allows it to absorb liquids that have been painted onto it – however, unlike regular paint that holds on to its shape when dried, the liquefied plastic drips down into the pores as well.
Because of this, painting over a piece of wood with plastic will always bond the two together. So if you're looking for a way to remove paint or varnish from your DIY project without damaging its original surface, then try using this method.