Welcome to the Shopify Community. Sorry to hear you're having troubles with your Oberlo App. When you head to your Shopify Admin > Apps, do you see Oberlo listed there? There is a screenshot of this below.
If Oberlo is not listed, click Customize your store in the top right hand corner (also in the screenshot). Then search for Oberlo on the App store, from there you should be able to reinstall it by clicking Add app.
If Oberlo is not in the list of apps in your Shopify Admin, and you're experiencing an error when you try to reinstall it on your store, please try following the steps to reinstall the app again through a private browsing or incognito window.
Let me know how this goes! If you're still having troubles, screenshots of your installed apps, as well as the error you receive on the app store would be helpful for troubleshooting.
Hilary | Community Moderator @ Shopify - Was my reply helpful? Click Like to let me know! - Was your question answered? Mark it as an Accepted Solution - To learn more visit the Shopify Help Center or the Shopify Blog