How can I call method from onPress on Alert function [React-Native]

First issue, the Button component has a title prop instead of having <Text> as a child. Second issue is that you have a bunch of syntax errors and are not calling functions (or binding) correctly. If you fix that, then it should work fine; for example:

alert = (msg) => {
  console.log(msg)
}

onDeleteBTN = () => {
  this.alert(' OnDelete')
}

render() {
  return (
    <View style={styles.container}>
      <Button
        title="Delete Record"
        onPress={() => Alert.alert(
          'Alert Title',
          'alertMessage',
          [
            {text: 'Cancel', onPress: () => console.log('Cancel Pressed!')},
            {text: 'OK', onPress: this.onDeleteBTN},
          ],
          { cancelable: false }
        )}
      />
    </View>
  );
}

Note:

• I don’t know what your alert() function is supposed to do, so I made a dummy one that logs to console.
• There are other ways of doing this like calling onDeleteBTN() or binding.