First off, dont scrape it off, suck it up airline tubing. The tubing is large enough to suck up the algae, yet you will not lose alot of water that you have to replace. Second, check your feeding amounts, cut back where you can. Use R/O water in your water changes and do all that you can to get nitrates and phosphates down.
I cannot stress enough that you need patience and diligence to combat cyano
and win. It is not something that will go away quickly. Getting cleanup crew creatures that specialize in cyano
will help. My personal favorites are sally lightfoot crabs and zebra hermits. Turbo snails will also help.