Create your page and nanoflows around a non-persistent entity like AccountPasswordData.
In your save nanoflow, check for internet connection and then call a microflow with NPE as parameter. Do the server logic like Ashishkumar suggests with current microflows and commit Account. Then use a selective sync in the microflow to update the Account object on device.
I hope you’re doing well.
In order to implement the change password functionality in Mendix Native Application, I’d recommend you to please check the functionality of change password in Account Overview Page.
Click on one particular user and check the change password functionality on it. I believe you can implement the same in Mendix however, you will need to work synchronization while implementing same logic in nanoflow.
I hope I’ve answered your query.