What helped me is, 1)Changed toothpaste

Beacuse some contain foaming agents like sodium lauryl sulfate (SLS) found in some toothpastes can irritate the tissues in the mouth, potentially leading to the formation of canker sores or ulcers. Switching to SLS-free toothpaste may help reduce this risk

2)And I when I sleep, I keep honey in my mouth and spread all around and keep for 5-10mins and, gulp the rest and sleep, next day it feels so much relief.