> How do you do that?
Great question. I assume you're asking from the point of view of the person having the challenge rather than someone observing/helping them.
There's no easy or painless answer. The reason these deep flaws exist in us is precisely because we have been avoiding dealing with them for some deeply personal and painful reason. But I do think there's a general pattern that I can share from my own experience.
The first step is to recognize that the problem exists and be "fed up" with it. To recognize that you're selling yourself short in some way, that you're failing yourself or your relationships. "I don't want to have my work and family life suffer anymore because I am afraid to talk to people." Or even "I don't want to be out of shape and struggle to walk a mile" kind of thing. You can't solve problems like this unless you're seeing them clearly and desperate to get out.
They often say that you have to hit "rock bottom" as a requirement for curing yourself. I think this is what they mean.
Once you hate the problem, it's good to get some external data. Ask your boss, colleagues, family about how you are (eg: tell me where my communication skills are weak, what am I doing that is so obviously wrong?) and then listen to what they say. They may surprise you? Eg is there a pattern, you are bad at it in some contexts and good in others? What is that about?
From the above and other resources, come up with the list of behaviors that would be an improvement. For example: "I would be better at my job if before I dive into a project, I speak to 3 people who understand the problem space" is probably a non-controversial one.
Then you ask yourself: why does that feel hard? Why am I just reluctant to get up and ask the sales person what the context of the client need is? What is it about "going up to someone I don't know super well and asking them a question" that terrifies me? What do I think would happen if I did this? Would they mock me? Would I feel like an idiot? Would they tell my boss I don't know something I ought to know?
Reflect if the fears are real. Is anyone in the work environment actually going to react the way your fear would suggest?
If intellectually you know that the thing is right and safe, then you force yourself to do it. Hyperventilate at your desk and then suck it up and walk over to the sales guy. Ask them, get the information, have a conversation. Reflect in retrospect: was this a helpful activity, and did I get hurt the way I feared I would?
Keep doing it. Build up the experience/muscle of doing the thing, and prove to your anxiety that it's not a dangerous thing to do. Talk to others who got good at this thing despite being not good at it originally. Find people who are awesome at the thing and study what they do. Become a nerd on the thing that's scaring you and you will likely see it stop being scary.
And I would be remiss not to say that in most cases, our deepest problems (even if they simply manifest in work performance) stem from psychology and childhood experiences. The guy in my story must have had some rough experiences growing up, maybe he was called an idiot or ignored or mocked or whatever, which made it hard for him to be communicative/open later in life, including with his family. Making a little crack in the armor of anxiety through the work process would help, but when something is this deep, seeing someone like a therapist is often helpful as well.
But to rewind, the key thing is to recognize a gap between how you are and how you want to be. You fundamentally have to say to yourself "I don't want to be forever limited by this thing, I don't want to hurt myself and others because of this thing" -- everything else is problem-solving.