You can't.
A replay can only be played in GT5.
If you want to get replays recorded, I suggest you get a Video Capture device.
You can use the basic ones like the dazzle video capture which uses the Yellow(Video), White(Left Audio) and Red(Right Audio) RCA plugs or you can get a HD-PVR which uses the Y(Green Plug), Pb(Blue Plug) & Pr(Red Plug) plugs.
The HD-PVR also has HDMI but you can't use that with the PS3 due to the HDCP encryption.
You can use it on an Xbox 360 though.
P.S Watch your grammar.