The easiest way would be to install Anki Desktop and
do it there. Most users find it much much easier to add cards with Anki Desktop anyway.
There is currently no way to change the deck override setting directly from AnkiDroid, so the only other way would be to switch to a different (or create a new) note type that doesn't have that setting turned on (it's off by default).
If you've never used Anki Desktop then presumably the note type came from a shared deck or a deck you received from a friend? Or perhaps it's a note type left over from a verrrry old version of AnkiDroid that a bug related to this feature.
FYI I personally consider this behavior as a bug, and I've sent a
patch to the developer of Anki Desktop, so it should hopefully be fixed in a later version of Anki.