I do oil pulling (as it's called) sometimes, not particularly for ulcers/gums, but because it draws toxins from out of the body (not just the mouth). What I have read though is to use just 1/3rd of a teaspoon, as the volume increases in the mouth as saliva adds to the volume, and, to do this practice for 15 minutes.

I mostly do the same with urine though instead of coconut oil as it has similar effects and cost $0. Do you know about urine therapy? I've written a few posts about it here, as have others:
https://peakd.com/search?q=urine%20therapy&sort=relevance&since=all