It might be handy to edit your question with the error you are getting. The microflow should retrieve the current user. Then retrieve the account for the current user and then pass that object to the change password form.
The first picture is the default microflow that was in the template. The second is the error message I receive after setting the change password menu item shown in the third picture. I read somewhere that I needed to Put the call microflow button in a data view container. The last picture is what shows when I trigger the microflow button in the data container. Hope this helps.