You can take it out and soak it 20 minutes in a 1:3 or 4 ratio of hydrogen peroxide 3% to water.
Or you can pull up in a syringe 1-3ml peroxide to every 1 gallon of tank water. Turn off your filters, then slowly squirt the algae with the peroxide. Leave filters off 20 minutes.
Reduce your lighting to 6 hours daily until it's been gone a couple weeks and then slowly increase lighting by 30 minutes every 2-3 weeks but if you see algae begin to develop then back you lighting down 30 minutes.
What size tank and what type lighting are you using? How long are you running the lights daily? What plants are in the tank? Are you using CO2
or liquid carbon? What about ferts? The thing is you can treat the algae and kill it but if you don't correct the problem causing it the algae will most likely come back.