Can an invention be patented if it isn't new?
While you can’t patent an invention that has already been patented, you may be able to patent a particular function or design of it.
A utility patent is appropriate for new or improved inventions. Of course, in your situation, it would be for an improvement on an existing invention and not a patent for a brand new idea.
A design patent doesn’t focus on the use of the product at all. Instead, it focuses on the ornamental features of it. So, if you are creating a brand new look to an existing invention, then this may be protectable under this type of patent.
Source: Quora