“How to treat gum swelling after a root canal?”

Sounds like inflammation at the root of the the root canal tooth. You should consult with the dentist who treated you.

Gum swelling after a root canal can be uncomfortable, but there are several ways to manage it. Over-the-counter pain relievers like ibuprofen (best) or acetaminophen can help reduce discomfort and swelling. Applying a cold compress to the cheek near the affected area for short periods can also provide relief. It's important to maintain good oral hygiene and avoid hard or chewy foods to prevent further irritation. If the swelling persists or worsens, or if you experience severe pain or fever, it's crucial to seek professional help from your dentist or endodontist.

The swelling is most likely from the clamp used to isolate the tooth, unless the tooth was swollen previously from the infection. If it is truly gum inflammation rinsing with salt water will help alleviate the swelling but it may need antibiotics as well. Speak to your doctor.