Use epoxy glue that drys clear. Fill the crack carefully and completely then put clear tape on it to flatten it out. Once it is dry scrape the top carefully with a razor blade to be the same height as the counter surface.
I have a plastic chair mat under my computer desk that the edges are curled and won't lay flat. Have been unable to bend them back as the plastic is hard
https://www.youtube.com/watch?v=lIRHMSj0G8A
Use epoxy glue that drys clear. Fill the crack carefully and completely then put clear tape on it to flatten it out. Once it is dry scrape the top carefully with a razor blade to be the same height as the counter surface.