Khechari alone is not enough.
Also there are two types of khechari, the one where you tongue tastes soma (when you shove it up ur throat) and the other one where tongue presses against upper palate.
The later one is to generate willpower.
Khechari should be practiced along with ujjayi breath and mula bandha, particularly pulling up kundalini from muladhara towards vishuddhi.
This is a type of pranayama which when done properly generates pleasant tickling in thyroid (1/3 orgasm kind of, similar to sneezing but prolonged)
Practicing this for a while allows you to anchor kundalini in vishuddhi and after this has been achieved you switch focus to ajna. Attain this and you will have no further questions about how and why.
Also, dont aim for tongue into your throat. Tasting soma is primarily for hibernation and exploration of mind realms while body metabolism slows down to nearly zero.
They used to clog all orifices with wax and burry the yogi alife after they attain the tongue drinking soma. I advise to focus on the other type. Just generate willpower and pull kundalini upwards.
Hibernation is the dead end.
P.S.
As with all yogic practices, approaching it as a physical exercise (i.e. sticking tongue into throat and waiting for something to happen) will yield zilch.
You need a mental component into it and this is where raja yoga/buddhism comes into play. You need theory for it to work properly, otherwise its all just pointless exersize.
Gate Gate Pāragate Pārasaṃgate Bodhi Svāhā