Ever since Valve decides to return the Side Shop to the Dota 2 Battle Pass after heavy backlash from its players, it has remained hidden to date from its user interface.
Here is a step by step guide on how you can access it once again!
Voila! This is how you can successfully access your hidden Side Shop. Naturally, the Battle Pass achievements that were related to the Side Shop were hidden as well. Battle points are rewarded if you combine every hero and upgrade it into a three-star in a single tier.