Simple - you stop.
When an object in motion is left to settle, it eventually comes to rest.
Tai chi only starts to work when the student stops trying and doing.
Stillness and silence cannot be forced.
Do you force your heart to beat?
Your body does not require your intervention.
When you cease doing, nature is allowed to act according to its own way.
Wu wei requires that you do not interrupt the flow.
Our approach to tai chi is concerned with feeling how the body wants to move and letting it move that way.