How do I sell my account to another player?

According to the game's main guidelines, this is prohibited. Such is even published in their help and support:

"Army Men Strike strictly prohibits buying or selling accounts, and trading any game items and resources etc. If a player violates the rule and decides to buy an account, the purchased account will not be protected by us. For your own interests, please do not participate in any form of unofficial trading. If we have identified players who buy or sell accounts, we may mute or even ban those accounts."

Hope this helps!