Competitive mindset, you either have it or you don’t.
But if you are willing to aim high, even if you don’t reach those goals, you will always end up in a better place than if you aim low and succeed.
So you want to do a Strongman competition?
Once you’ve found a gym, message them, ask if they have a Saturday or Sunday group training session that you can come along to. Most gyms will have a group of lifters who get together at the weekend for events training and will be more than happy to have you come along.