In the Lightroom tab, select the albums view drop-down menu, and then scroll to Your albums.
In the Your albums list, select the album to open it.
Select and open the photo you want to set as the album cover in the Detail view.
Select More > Organize , and then select Set as album cover.
You can repeat this process at any time to select a different cover photo. If the album is saved in a folder, select the folder first, then select the album to set its cover.