Hi Tuctuc3,
Thank you so much for kindly taking the time to create a support thread.
Regarding your issue, please be sure that you are signed in as the administrator in the WooCommerce account, and you are connected to the correct store you wish to remove such plugin, then search for the Omnisend plugin in your plugin tab. Once there, please be sure that such is deactivated first and then choose the option to delete the plugin. If this does not result successful, we ask you to please clear your cache and cookies and try once more.
If you should need any further assistance, please feel free to reach out to our support team at [email protected], where our team will be more than happy to assist.
We look forward to hearing from you and wish you an amazing rest of the day!