Did you already send NAU tokens to eth addesses?
"To use your NAU wallet, you would be required to download NAU application (Android or iOS) and sign in with this phone number (we will create an account for you and link it to this phone number). " Is this wallet mandatory to receive tokens?
The official NAU app is used to manage NAU coins. If you choose to exchange them to eNAU, you may use whatever ERC20 compatible wallet you prefer.