By default, two app shortcuts are displayed in the bottom corners of the lock screen on Samsung devices. These include the phone app (left) and the camera (right). If desired, these can be bundled together as a single shortcut or hidden completely. Samsung also allows apps to be exchanged, so app shortcuts from Facebook, WhatsApp or any other app can be placed on the lock screen.

Android 10 (One UI 2.0)
Step 1:  Open the  Settings
Step 2:  Tap on  Lock screen
Step 3:  Tap on  Shortcuts
Step 4:  Tap on  Left shortcut  or  Right shortcut
Step 5:  Tap on desired  App
  1. Open the Settings
  2. Tap on Lock screen
  3. Tap on Shortcuts
  4. Tap on Left shortcut or Right shortcut
  5. Tap on desired App

Samsung Instructions