thanks for asking your query
is due to multiple reasons like poor oral hygiene
,crowded teeth leading to palque accumulation,vitamin C
deficiency,any medication,irritation,inflamation,any infection,gastric disease...
you can improve your swollen gums by eating a healthy balanced diet.
maintain very good oral hygiene,brush twice a day and floss regularly
gargle with saline water
use antiseptic mouthwash
take vitamin and iron supplements
yourself,because high level of stress impact hormones which cause swollen gums
avoid tobacco and extreme foods/beverages
hope this will help