UI Scripting in AppleScript

Open the “Accessibility Inspector” app to try to determine each element

Example with some UI Scripting for Messages app to set the default send address:

    tell application "Messages" to activate
    
    delay 1
    
    tell application "System Events"
        tell process "Messages"
            click menu item "Preferences…" of menu "Messages" of menu bar 1
            click button "iMessage" of toolbar 1 of window 1
            click radio button "Settings" of tab group 1 of group 1 of window 1
            --open "Settings" tab of group 1 of window 1
            
            set SendFromPopUp to pop up button 1 of tab group 1 of group 1 of window 1
            click SendFromPopUp
            click menu item "user@icloud.com" of menu of SendFromPopUp
            
            click button 1 of window 1
        end tell
    end tell

Handy reference: https://n8henrie.com/2013/03/a-strategy-for-ui-scripting-in-applescript/