Select an item from dropdown and use that value in another component in React native

Just do something like this:

navigation.navigate('RouteName', { /* params go here */ })

You might want to read the following documentation: https://reactnavigation.org/docs/params/

You can do that like:

const onPress = () => {
    try{
        const topic = "Plant/type";
        ...
        navigation.navigate('Air', {newTopic: topic}) //you can pass another value by separating with comma
    }catch(err){
        console.log(err)
    }     
}

Then you can fetch the same value in next screen like:

function NextScreen({ route, navigation }) {
    const topic = route.params.newTopic
}

Hope this works for you.