Question

A man can swim in still water with a speed of 2m/s

Answer 1

then he can swim down the flow as 2+v and up the flow as 2- v

Answer 2

A man can easily swim in the stagnant water at a specific velocity of the 2m/s.

To do so,the swimmer only have to apply such amount of force in the water with his hands and feet ,to create a repellent force from the water, according to the third law of attraction the Newton.

Here,the water flow's velocity is zero itself that's why it doesn't matter the velocity of the swimmer.