I would suggest a few things. First, be genuinely open minded to the discussion/topic (as in your opinion can change with a good enough argument.
Second, I would suggest using "feeling" language as much as possible. Examples are: "I feel like that will cause an issue with...", "my understanding is...", "my thoughts are...", "from what I've seen/read the setup is ...", etc. From my perspective, feeling language lowers the "absoluteness" of statements and makes conversions easier by changing them from arguing absolute truths, to discussing lived experiences.
Third would be to reframe the discussion/argument from "you vs them" to the two of you vs a problem/issue and you both are working together to find the answer. This somewhat goes with being open minded.
Fourth, I don't think works too well in online discussions, but in person I find starting from a base situation and asking the other person their thoughts on it, and adding your own, works well. So, start with a base situation and then adding a little complexity each time you both agree on the outcome and reasoning. Once you've found your divergence point you can start having your discussion about the pros/cons of different approaches/solutions to that specific situation.
Yeah, it definitely feels, to me, like the current world/society is built to be competitive rather than cooperative :(