Is My Brain the Enemy?

I find myself thinking my brain is the enemy because it keeps presenting thoughts that don’t serve me. Which is an unhelpful thought itself I realize. But if my brain keeps thinking thoughts that lead to results I DON’T want, how is it NOT the enemy? Re-training my brain so that I think it is my ally seems really hard and like it is going to take a long time. I know– more thoughts. How/what can I do to shift this so I feel like my brain is working with me instead of constantly against me?