You have the same challenge when writing from a limited third person perspective, because unless you’re using more than one or two points of view, there’s bound to be important action happening where the main character is not.
First of all, you have to ask yourself, how important is this scene/event going to be to the story? If it’s not vital, your first person perspective gives you a great excuse to cut it out, or at the very least to pare it down to the information that’s really crucial.
IF you really do need it, there are ways. In one book, an important plot point was the occupation of a certain city by peacekeeping forces. My main character wasn’t there, but she watched footage of the event on TV.
At other times, I’ve had secondary/supporting characters play the role of info bringers to the main character. For example, one main character wasn’t present for an important family discussion, but her brother was, so she learns the information from him (by eavesdropping on a conversation she wasn’t meant to hear, I might add.)
Depending on the time period or genre, you could use telephone calls, letters, visits from relatives, magical communication devices, time travel…the possibilities are endless.