IRL, charisma is a learned skill, not a genetic trait. So, IRL, you can increase your charisma through a variety of means.
If you don't grow up in a family where these skills are taught from an early age, then you can take classes and workshops to learn them. Or you can learn them experientially.
You can take workshops to learn how to manage small-talk more gracefully. Or join clubs like Toastmasters to practice giving presentations and speeches. You can take classes in etiquette.
You can have a mentor who sits next to you at a banquet and quietly coaches you on appropriate conversational topics and good manners. You can stay with the family of a best friend or romantic interest and learn by observing how to be more charming.
If you are on the spectrum, you can learn to keep eye contact and other social skills that may not come naturally.
Everyone can increase their charisma by discovering the techniques that help make other people feel comfortable and listened to. Practicing them on a daily basis will make you more charismatic over time.
So the increase can be either slow and incremental, or sudden and noticeable. Or both.