A bridge has a fairly simple directive to fulfill: be different, create a contrast, and make the listener long to go back to another section. Just like a real bridge, it takes you from one place to another. It connects song sections and moves to a different level of information than the other sections. It’s an opportunity for a new perspective. Sometimes in the form of a question. Musically, it’s a chance to offer the listener something they haven’t heard before.
A bridge can focus on any kind of material: specific, abstract, philosophical, internal landscape, external landscape, emotional reaction, metaphorical interpretation, etc. But it should not move the story forward like the verse does. It is not the bigger picture, like the chorus.
A bridge in a verse/chorus song usually occurs after the second chorus, often leading to another chorus, though it sometimes leads into another verse. In verse/refrain songs, the bridge usually occurs after the second verse/refrain.
Tools to write Bridge
Look at the main message of your chorus, probably your title. Question it. What if xx wasn’t true? What if xx didn’t happen? How can I live without xx? What can I do to change or fixxx? Or have a wake up call: why does xx matter? Let go of xx. Come at it with a different perspective. Go deeper.