You can use the features of the mobile app by signing in to your planBIM account. There are two ways in which you can do that.
Sign in through email address
If you are a planBIM user, you can sign-in directly on the mobile app by entering your email address as shown below, and then tap on NEXT.
If you haven't created an account with planBIM, you can refer this article to help you create one using the mobile app.
If you have set up your account without using any social links previously, you will now have to enter your planBIM account Password and tap on SIGN IN.
Sign in through Social Links
The app also lets you choose social mediums such as Google and LinkedIn as options to sign in to your planBIM account. Once you tap on any one of these icons as shown, the app will redirect you to the sign-in page of their respective accounts.
After following any of the sign-in procedures listed above, you will be able to access your planBIM projects.