I have a smal lump attached to a nurve tenden under my left arm pit. My arm goes numb.

I have a small lump attached to a nurve tendon under my left arm pit

We can't guess what your lump is. There are lymph nodes in the armpits, which swell when they are fighting infection. It could be pressing on nerves that make your arm go numb, so see a doctor. There is no such thing as a nerve tendon.