Whenever you can, steer the conversation to the changes you are making or have made. Don’t tell your ex “I am making changes” or “I have changed”, it’ll come across as ‘selling”.
You’re ex will likely tell you “don’t change for me” or “I am happy for you” because nobody likes being sold to.
Instead show your ex how you’ve changed by not repeating the behaviours that caused problems (and the break-up) and by being better as a person and as a partner.
If your ex doesn’t see himself or herself in a better relationship, they’re not coming back. But if you handle this right, it won’t be long before you see changes in your ex’s attitude towards you.