Problem of changing Android encryption algorithm to update app on Google Play - from AES/ECB/PKCS5Padding to AES/GCM/NoPadding

The rejected code is as follows.

public SecretKeySpec generateKey(int keySize) {
   Date date = new Date();
   Random rand = new Random(date.getTime());
   byte[] aesKeyData = new byte[keySize];
   rand.nextBytes(aesKeyData);
   SecretKeySpec aesKeySpec = new SecretKeySpec(aesKeyData, "AES" );
   return aesKeySpec;
}

public byte[] encrypt(byte[] data, SecretKey key)
   throws NoSuchAlgorithmException, NoSuchPaddingException,
   InvalidKeyException, IllegalBlockSizeException, BadPaddingException {
   Cipher cipher = Cipher.getInstance("AES/ECB/PKCS5Padding"); //here
   cipher.init(Cipher.ENCRYPT_MODE, key);
   byte[] outputBytes = cipher.doFinal(data);
   return outputBytes;
}

public byte[] decrypt(byte[] data, SecretKey key)
   throws NoSuchAlgorithmException, NoSuchPaddingException,
   InvalidKeyException, IllegalBlockSizeException, BadPaddingException {
   Cipher cipher = Cipher.getInstance("AES/ECB/PKCS5Padding"); //here
   cipher.init(Cipher.DECRYPT_MODE, key);
   byte[] outputBytes = cipher.doFinal(data);
   return outputBytes;
}

This is the problem part. (i guess...)

Cipher.getInstance("AES/ECB/PKCS5Padding")

If I change this part to the following, I expect the problem to be solved.

Cipher.getInstance("AES/GCM/NoPadding")

However,
existing app users have encrypted data using "AES/ECB/PKCS5Padding".
So, after decrypting with "AES/ECB/PKCS5Padding" in the newly distributed app,
user data need to encrypt it with a new algorithm.

In this case, my new app should contain the existing algorithm that is rejected in Google Play.
Then, I guess, Google Play will do the same reject.

What should I do to solve this problem?