Very simple job. You have to break the sight glass by tapping it with a center punch or screw driver. Don't hit it too hard otherwise the shattered plastic can go in to the sump. Then pull out the broken bits and the seal with some pliers.
Clean up the whole area make it nice and dry and then put some oil on the rubber seal on the new sight glass seal. Using a suitable sized socket , I think it's 17mm, tap the new sight glass into place and you are done. Take note of how flush the existing sight glass is before removing it so you know how far to tap the new one in. It's a 5 minute job.