if (currentUser!= null) { if (!mEmail.isEmpty() || !mPassword.isEmpty()) //checking email,password editText are not empty { AuthCredential credential = EmailAuthProvider.getCredential(mEmail,mPassword); currentUser.linkWithCredential(credential) //linkWithCredential is a method provided by Firebase just to link the credentials .addOnCompleteListener(new OnCompleteListener<AuthResult>() { @Override public void onComplete(@NonNull Task<AuthResult> task) { if (task.isSuccessful()) { Toast.makeText(LinkAccount.this,"account linked",Toast.LENGTH_SHORT).show(); } } }) .addOnFailureListener(new OnFailureListener() { @Override public void onFailure(@NonNull Exception e) { Log.e("TAG2",e.getMessage()); } }); } }