By default, the album overview on the Samsung device always uses the latest image in the album as cover. Alternatively, you can select a cover image which is always displayed. The cover image can be changed at any time or you can also undo the change to the latest image.

Android 10 (One UI 2.0)
Step 1:  Open the  Gallery -App
Step 2:  Tap on  Albums
Step 3:  Tap on desired  Album
Step 4:  Open the  menu
Step 5:  Tap on  Change cover image
Step 6:  Select desired  Cover image
Step 7:  Tap on  Save
  1. Open the Gallery-App
  2. Tap on Albums
  3. Tap on desired Album
  4. Open the menu
  5. Tap on Change cover image
  6. Select desired Cover image
  7. Tap on Save

Samsung Instructions