Hey Jingli 

Thank you for posting in the Lucid Community! To clarify--is the share button on the folder gone or not working? By clicking share you can manage the collaborators of the folder. To do this click manage in the bottom-right corner of the pop-up window. 

If the share button is gone or not functioning properly would you mind to try again using an incognito window? 

Let me know if either of these options help! If not you can always reach out to us at support@lucidchart.com so we can take a closer look. Cheers!