How toget rid of armpit pimple its been days?

Have it evaluated. The area has hair roots that can become inflamed & abscess. It has apocrine grands that can develop similar abscesses. Some will respond to moist heat and resolve without other treatment. Some will require surgical drainage to heal.

Fill your bathtub with warm water and pour half a cup of Clorox . Bathe in it , as long as you can and try to express the pimple when you are in the tub. This water is not harsh and helps to kill the Staph Aureus. DAB a bit of Benzoyl Peroxyde 10% at night on the pimple and sleep with a white T-shirt. If in 5 days it’s not improving but getting worse, bigger & more red, go to the ER for drainage