All you have to do is write, "I walked onto the bridge" instead of "Kirk walked onto the bridge."
If you're doing multiple first-person POVs, that's not
all you have to do. You also have to establish right up front that you've changed to a new character's viewpoint, so you don't confuse the audience. Say, for instance, you've just been in Spock's POV and you switch to Kirk's. You'd have to make sure the first sentence was something like "I walked onto the bridge, tugging the hem of my gold command tunic, and turned to Spock." But that can quickly get awkward. As Greg said, it's not something that should be attempted unless you're experienced. And the potential advantages of it are elusive. It's easy enough to get into multiple viewpoints from an omniscient third-person perspective, since you can still eavesdrop on your viewpoint character's thoughts; and there you have the advantage of using the character's name rather than just "I," so it's clear to the reader who the viewpoint character is. So why not just use that? Multiple first-person viewpoints seems more like a gimmick than something that would really be useful to a story. The only value I can see for it is in an overtly epistolary narrative like Dracula