Is it unlawful to intensely play with the navel until one feels cold, relaxed, and trembles, accompanied by vaginal discharge without touching the vulva? And how can one get rid of this act?

As long as you are doing this with the intention of achieving pleasure by ejaculating semen, this act is considered masturbation, which is forbidden, whether it is done by hand, or by other direct contact, or by looking, or by thinking. This is because the reason for the prohibition is the spilling of semen and the incitement of lust in an impermissible way without excuse, and because satisfying lust is not permissible except with a wife or a slave woman. So, whoever seeks beyond that is among the transgressors. The Prophet, peace be upon him, guided those who could not marry to fasting, and did not mention anything else. Therefore, you must hasten to repent and regret this act.