Hello & Welcome to Just Answer,
Sorry to hear of any issue you may be having with your phone or greeting.
If the one greeting is already on the system, to change it you simply need to record a NEW greeting and it will replace the old one.
NOTE: This recording usually has to be done using a cordless handset (vs. the Main Base Unit).
I have a link to a video that shows the steps to make this new greeting and what you can expect to happen when you do it.
Please take a look at the entire video (just over a minute long) and then try the same steps on one of your handsets.
Click Here for Video --> https://www.youtube.com/watch?v=xqnQLiaGO7Q
Please let me know if that works for you or if you have any more questions.
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Thanks, ***** *****