Buy a 10k ohms volume control with an audio taper (logarithmic). Do not use a linear potentiometer. An audio volume control will probably be marked "10k A" and a linear pot will probably be marked "10k B".
Connect one resistive terminal to ground, the other resistive terminal to the output from the receiver and the slider to the computer audio input. If its wires are longer than a few inches then they must be shielded audio cable or they will pickup mains hum.