how to change input method with ime command
The ID of an IME isn't just the class name. Multiple packages, signed by different developer certificates, might use the same class name. That's especially likely in this case where it's a downloaded example. You need to use both parts of the ID, before and after the /. In this case:

shell@android:/ $ ime enable com.thihaayekyaw.frozenkeyboard/com.example.android.softkeyboard.SoftKeyboard


Note, though, that ime enable doesn't select that input method: it merely allows it to be selected by checking its checkbox in the IME list in Settings → Language and input. To select an IME (i.e. to make it the one that will appear when an EditText is focused) you need to use ime set:

shell@android:/ $ ime set com.thihaayekyaw.frozenkeyboard/com.example.android.softkeyboard.SoftKeyboard