You need download the app as a mobile web app, click EXPORT > HTML/JS/CSS:

Download the project and unzip it. The folder should contain package.json. From inside this catalog, start npm install (you need to have node.js and npm installed): all the dependencies will need to be installed from package.json.

Then run ionic serve which will start the project preview.

ionic build --prod will create the project build that can be then uploaded to whenever you need it.