The project navigator is the left most column in the Xcode editor, click the topmost item in the project navigator, then move to the next column on the right of the project navigator, there will be two items in this column, one labled project, and one labled targets, select the targets item, then move to the right again on the displayed screen to the next column / pane, there will be five tabs near the top, just below the main toolbar, they will be labeled Summary, Info, Build Settings, Build Phases, and Build Rules, select the Build Settings tab and there will be a text search bar just below the tabs, enter your error text in this field, and the settings for that search will appear below the search field.
Also when asking for help with Xcode, tell us what version of Xcode you are using, as there are slight differences between Xcode versions, the advice above is for Xcode 4.2.
Hope this helps.
Regards Mark