Milestone Bar is refreshing to the first milestone on the click of a button

Certified Senior Developer

Hi Appian Devs, 
Please have a look on the interface snippets below where I have implemented a milestone bar:

I have a milestone bar with 2 milestones, In the first milestone(which is default selected) when I click on the link to download contract link, I see the following link,

Once I downloaded the file with the downloaded link, I got the file, after that,  I will click on Milestone bar 2 for uploading the new version of the file as below:

Now I uploaded the new version of the file as below:

There is a button which replaces the current file to the uploaded file and makes it latest in the variable
But once I hit the button, It refreshes the milestone to the previous milestone as below:

I want to retain the second milestone step even after the button click 
Please let me know the right directions for the same


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