The phrase "fixed one's wagon" is an idiomatic expression that means to cause trouble or get revenge on someone. Antonyms for this phrase could include words like aid, assist, support, aid, help, protect, and defend. For example, instead of trying to fix someone's wagon, you might offer them assistance or support to help them through a difficult situation. Alternatively, you might choose to protect or defend them from harm rather than seeking revenge. The opposite of fixing someone's wagon is to act kindly and compassionately towards them, rather than seeking to cause them harm or trouble.