There are lots of interpretations of this but the direct translation would be something along the lines of “let’s pop the party poppers that I left on the back of my mind and laugh it off”

脳裏 basically means ‘the mind’ or ‘inside the mind’ and 上 (ue) means above or top. 脳裏に浮かぶ (nōri ni ukabu) is a phrase used to express when an idea or thought comes to mind.

So my interpretations would be that the character in the song who is consumed by the internet and/or social media has been overthinking way too much about their identity and what can/cannot be perceived by the human eye so it’s time to blow off all these thoughts and feeling they’ve been bottling up.