There is no Highcovery app for Shopify. You set up affiliate tracking yourself by copying two scripts into your theme and creating four webhooks. A wizard in the dashboard guides you through the steps, see Set up Shopify. Nothing needs to be done on this page for that.
Only one platform can be active per online shop. If you select a different platform, the existing connection is disconnected. The dashboard asks for confirmation first.
If you already take part in the affiliate programme, the platform is locked as long as it is active there. In that case contact support@highcovery.com.