A reader has a Facebook emergency:

” I was messing around with my Facebook settings and clicked on Limit Past Posts setting. Now, my share button has disappeared!  Can you tell me how to reset this setting permanently or to change it to make a specific post shareable when a friend asks me to?  Please, I really need your help.  I have spent hours and hours trying to find the answer on the internet, but they never seem to work.”

First, I’ll explain how this setting works for those who aren’t familiar with it.

The Limit Past Posts settings is pretty handy. It allows you to go back and control who can see posts you’ve made in the past. To start, open Facebook in a browser. It doesn’t matter which browser. Click the arrow that looks like an upside down triangle at the top right.

Choose Settings from the drop-down menu.

When Settings opens, click on Privacy at your left.

Under Your Activity and select Limit the audience for posts

If you click on Limit Past Posts, all posts on your timeline that were shared with a a wider audience than your Facebook friends will be limited to just your friends.

Unfortunately for the reader who asked the question, once you make the change, you can’t undo. You’ll have to go back and adjust the privacy settings of each past post individually. So think about this setting before you make it final.