Welcome to the Shopify Community. Sorry to hear you've been experiencing issues with an app you're trying to install. To clarify, is this the Pickerr app you're trying to install? What exactly is the issue, are you able to please provide some more information such as where you're getting stuck, or any errors you may be receiving?
In general, this is a third party app, and therefore for integration issues, your best point of contact will be the app developers themselves. If the app I linked above is the correct one, their contact email address is listed as email@example.com. You can find these details on the app description page, under Support. There you can also find a link to their FAQ page. I'd recommend looking through their FAQs to see if you can resolve the issue before contacting them.
Can I ask why you're looking to integrate with this app? Or what specific features you're looking for? Just curious!
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