Do you have an airstone? You need more surface agitation to get it circulating. I would also do a water change and vacuum really well. The biofilm is usually from decaying food/waste on the bottom. We all get it, it's just that with proper surface agitation it won't build up like that.
You can get a cup and slowly scoop it off the surface before you vacuum if you want. A paper towel works too. I was told to lay newspaper on top and peel back gently to remove mine, but I never tried it. The airstone was what ultimately worked. (Back with my first tank)