i mistakenly didnt allow my iphone to connect to my macbook pro. how can i change the settings?

I would suggest disconnecting the iPhone from the computer

Then attach it again and this time click " Trust this Device " or something along those lines

Additional info regarding Sync to Computer for macOS 10.15 Catalina and Above >> Finder

Use the Finder to sync your iPhone, iPad, or iPod touch with your Mac - Apple Support (CA)

In Privacy & Security System Settings, set it to Ask Every Time in the "Allow accessories to connect."

For an iPhone that I had already allowed, it asked again when I connected it. I'm hoping it works the same for rejected devices.