From the Actor Classes tab (same window as the Content Browser), drag and drop a VehiclePickup_Boost_TA on your map. Then from the Scene tab, select the VehiclePickup_Boost_TA and change the Boost Amount parameter to be 0.12 and the Respawn Delay parmeter to be 4.
It will be invisible so add a mesh at the same Location to represent the boost pickup.
To try it out in RL, go to training -> tutorial -> basic, that has limited boost.