Thanks for posting the query,
Swollen gums indicates infection of gums and abscess
formation. As you said Root canal treatment is not completed, vital pulp tissue might be left in the canal causing pain and discomfort. Swelling of the gums indicates that the infection had spread to surrounding tissues leading to formation of abscess .
Antibiotics and analgesic
will give temporary relief ,
Get the abscess drained by the Dentist
and the root canal procedure completed
Unless the tooth is devatalised , disinfected and sealed to the apex you may experience pain and infection.
You maintain a good oral hygiene , use lukewarm saline gargles , use chlorhexidine
mouthwash gargles twice daily.
Hope this helps out.