The "Reset Mailchimp connection" link on the Mailchimp Settings page of your store Admin area (My Apps > Mailchimp Integration with eCommerce Support) serves to update connections in your online store or update the Mailchimp API key due to Mailchimp account changes.
Updating Mailchimp Connection and API Key
To update connections:
You will need the username and password for the Mailchimp account for connection, so make sure you have them ready. You will also require an API key that your store will use to access that account on your behalf, so ensure an API key has been generated as per the instructions in the Mailchimp knowledge base article About API keys.
On the Mailchimp Settings page in your X-Cart store, click on the "Reset Mailchimp connection" link next to the Mailchimp API key field.
On the page that opens, enter the correct Mailchimp username and password and choose to log in.
After successful authentication, the store will be disconnected from the old Mailchimp account and connected to the new one you specified.
Deactivating Mailchimp Add-on
If you wish to stop using X-Cart's Mailchimp integration, you can deactivate or uninstall the add-on in your X-Cart store.
Deactivation stops the add-on from functioning, but it does not remove the settings you made to the add-on configuration or clear any data generated or collected when the add-on was in operation.
If you wish to remove all the data related to using the add-on completely, you need to uninstall it.
To deactivate or uninstall the Mailchimp Integration with eCommerce Support add-on, follow the Managing Add-ons section's guides.