City Supply: commander can use “City Supply”to recover all troops that need supplies in Admin Area; the city will also recover all troops that need supplies automatically every one hour.

Be aware that air and navy troops have to get in Air /Naval  Force base to receive city supply.

Air Supply: League City can use "Air supply" to recover ground troops that need supplies in Admin Area.

Tactic Supply: player can use “Airdrop Supply” tactic to recover all troops everywhere.

(Tap the card icon right hand of the battlefield then you can find this tactic.)