Go to "My Account" (top left), there to "Projects" and choose your project, click on the name.

If there's noting there, your project is not yet connected to the community.

Once your project ist connected and you can access it in your Account, you can add your purchases there.

After that, log into the dashboard of your website and visit the "install"-page in the lower area of the dashboard. There you should find your add-on, download and install it.

Hi - I am also trying to install an app that I just purchased. I have associated it to the project and I have gone into my web site dashboard and to the option extend concrete5 and it shows that it is associated with the community project page: but I can't see the app to install. Any ideas where this is going wrong for me?

Did you purchase a license that is valid for your version of c5? There have been some people with this issue where the Add-On is for 5.6 and the site is 5.7 or the opposite.