You need a kit to bleed that brake.  Disc Brake Bleed Kit
It is one of those tools/kits that as an individual it is not worth buying. 
Even on Amazon the kit it $40.

A (quality) bleed replaces the fluid. 

Hydraulic brakes feel loose
Do you say Boruch Shepatrani for a girl at her Bas Mitzva? If not, why not?
