To delete the custom widget in the designer, click on the Settings icon in the Bold BI Server as shown in the image below:
Click on the Widgets
tab as shown in the image below:
You can delete the custom widget by clicking on the delete icon as shown in the image below:
NOTE: The custom widget will only be deleted within the particular tenant. This feature is available in On-Premises Deployment but not in Syncfusion Managed Cloud Server.