Once the icons on the Samsung device have been changed, the only way to reset them to default is to use Galaxy Themes; there is no option to change the icons to default in the usual settings.

Android 10 (One UI 2.0)
Step 1:  Open the  Settings
Step 2:  Tap on  Themes
Step 3:  Open the  menu
Step 4:  Tap on  My stuff
Step 5:  Tap on  Icons
Step 6:  Tap on  Default
Step 7:  Confirm with  Apply
  1. Open the Settings
  2. Tap on Themes
  3. Open the menu
  4. Tap on My stuff
  5. Tap on Icons
  6. Tap on Default
  7. Confirm with Apply

Samsung Instructions