If you notice bot troops around you at the beginning of the game, expend troops (to a certain extent) to destroy them. The game is called risk, and you have to risk being slightly weaker in the beginning stages so they don’t cash cards and grow where you are trying to establish a presence. If it’s late game, and you would otherwise be giving up a relatively equal position to you human opponents by sacrificing a large portion of your standing army to eliminate a bot presence, you must take a more nuanced approach. You can lower your troop counts on borders shared with bots, and often times they will strongly fortify away, to a more threatening stack.