Decide the date before you announce
Pick the end date, the last day of support and what happens to data. Customers cannot plan around a date you might move. If the date is uncertain, say what you know and when you will update them.
Give notice that fits the use
A feature people use daily needs more warning than one almost nobody touches. Look at who actually uses it and give those customers a direct message as well as a public post.
Explain why in plain words
Say what changed and why the feature is going. Customers accept a reason such as cost, safety or low use. They resent being told it is for their benefit when it is not.
Offer a way forward
Name the replacement or the closest workaround and say what it cannot do. If there is no replacement, say so honestly and explain how to export their data. Link a short guide for the move.
Prepare the team and the replies
Write a saved reply for the common questions, brief everyone who answers tickets and tag every conversation about the change. Agents should not improvise dates or promise exceptions.
Follow up before the deadline
Message the customers who still use the feature a few weeks before the end date, and again close to it. Then confirm afterwards that it is gone and say where to get help.