You will find the Cerustop (or C Stop) located under the dome, which will need to be removed first.
Your replacement C stops are in a grey pack containing 8 matchstick sized black sticks
Open the pack as you would a purse to reveal the black sticks containing the replacement C stops
Remove one stick. One end will have a barb on it, the other will have the white replacement C stop
Insert the empty barbed end squarely into the C stop you are going to replace.
You do not need much pressure and should feel a gentle click
Pull the whole stick backwards which will then come away from the receiver with the old C stop attached.
Turn the stick through 90 degrees and offer up the new C stop to the now empty receiver. Push it squarely but gently into the receiver.
You should feel another small click as it locates
Pull the stick backwards squarely leaving the new C stop in place, and discard the whole stick with the old C stop still attached.
Replace your dome.
‘Hear Clear’ is a similar device to the C Stop, and works in a very similar way. It is provided on Starkey products. The only variation to the procedures detailed above is that the removal of the Hear Clear requires the matchstick to be gently screwed a turn or so into the blocked Hear Clear wax guard rather than just pushed in.
After insertion the matchstick element is simply pulled out to remove it from the newly positioned Hear Clear.