The Conversions API Gateway data pipeline will only allow Meta Pixel as a data source, and Meta Conversions API as a data destination. You can manage your data pipelines in the Data pipeline page, including creating and deleting pipelines.
Click the name of the Conversions API Gateway data pipeline and go to the pipeline details page. Then find the Actions drop down button on the top right corner, and click Delete pipeline.
You can also delete a Conversions API Gateway data pipeline from either the Data source or Data destination tab. Click the Meta Pixel data source or data destination, and find the Actions drop down button on the top right corner, and click Disconnect pipeline.
Upon clicking the Disconnect Pipeline button, a pop-up window will appear to guide you through the deletion process to its completion.