“Is gum bleeding a sign of gingivitis, and how can it be reversed?”

Sounds like possible periodontal disease and should be evaluated by a dentist with X-rays and an exam

Yes, bleeding gums are often an early sign of gingivitis, usually caused by plaque buildup.
You can reverse it by brushing and flossing daily, using an antibacterial mouthwash, and getting regular dental cleanings.
If it persists, see a dentist to prevent progression to more serious gum disease.