Go through this guide backwards and reassemble the camera. Be careful reattaching the ribbon cables they can be a little fiddly, if you have large hands you might want to try using a pair of tweezers to line them up.
If like me you did this conversion at night, you may not be able to see anything, the lights in my house (LEDs) give off little to no IR light.
Test it by pointing a remote control at the camera and see what it picks up.
The image if you have one will likely be very red, so you need to set a custom white balance. Take a sheet of white paper and use that.
The cameras flash may give off a bit of IR light too, it should work.
If you have any (unacceptable) dust on the sensor, take it apart again and blow the sensor with the canned air. If you are careful it should be ok.