I find it hard to apologise to my spouse even for small things. How do I train myself?

Apologising first is not a sign of defeat, but a sign that you value the relationship more than your ego. Reluctance to apologise usually comes from embarrassment or fear of looking weak, not because you are truly blameless. Start with a short, honest statement: ‘I'm sorry about earlier, I was wrong.’ It does not need to be long or come with excuses to defend yourself. Practise on small things first so it becomes easy when something big comes along. People who correct themselves quickly are respected more, not looked down on. See communication & emotions.