Only run something once

I know the title might throw you off but what I am trying to do is detect when a play is in a certain radius of an armor stand and if he is then give him a tag ig the player has the tag and is in a 5 block radius setblock a chest with and nbt of items but when I put this in my tick.mcfunction it just continuasly setblocks the chest and I only want the chest to be set once