it's not brain surgery idiom
humorous这不是给大脑做手术（用来表示说话者认为…做起来并不困难或难以理解）
used to say that you do not think that something is very difficult to do or to understand
Just keep calm and do it. It's not brain surgery. 保持镇静，就这么干就行了，这又不是大脑手术。
Compare: it's not rocket science (rocket science)