You can apply to become a seller on Amazon seller mobile app by following the steps below:

1. Download Amazon seller app: Please search for "Amazon seller" app in your mobile app store and download and install it.

2. Register or log in to your account: If you do not have an Amazon seller account yet, please click "Register" and follow the instructions to fill in the necessary information to create a new account. If you already have an Amazon seller account, you will need to enter your login information in the app to log in.

3. Complete personal information: After logging in, you will need to provide some personal information and store information, such as your name, contact information, store name, etc. Follow the instructions of the app to complete this information.

4. Select seller plan: After filling in your personal information, you will need to select your seller plan. Amazon offers different types of seller plans, and you can choose the appropriate plan according to your needs and business model.

5. Complete store settings: After completing the seller plan selection, you will be asked to fill in more store settings, such as goods delivery method, payment method, refund policy, etc. Please fill in this information carefully to ensure a smooth transaction.

6. Submit your application: After filling in the store settings, you will need to check and verify your information. Once confirmed, you can click "Submit Application" to send your application to Amazon for review.

Please note that it may take some time for Amazon to review and process your application. Once your application is approved, you can start selling your products on the Amazon Seller Mobile App.