Adding an app to your watchlist is one of the basic steps you should take - as we suggest. This would ease up your work by saving your data and progress so that you don't have to search for the same app in the next session.
Basically, what you do is to search with the app name or id of the app you're looking for in the search bar on the watchlist (you can also search for an app in almost every page but we save that data within the session only). Watchlist opens up like a drawer from the left-hand side of the dashboard if you click on the arrow or the 'Add New App' button.
After you find the app, you just click on the plus sign to add it.
To add your app with the ID:
Find your app link on the Apple AppStore or Google Play Store.
Find your app id with followed by
id. (AppStore) copy only numbers or after id= (Play Store) part.
Paste your app id to the search-box.