How to remove third party application nintex from my sharepoint online?

 There are a few steps you can take to remove a third-party application, such as Nintex, from your SharePoint Online environment:

            

Remove the Nintex license from your Office 365 admin center. Go to the License section, then select the Nintex license and click on Remove.

Remove the Nintex App from your SharePoint sites. Go to each site where Nintex is installed, then go to Settings > Site Contents > Click on Nintex app > Click on Remove.

Remove the Nintex features and solutions from your SharePoint farm. This can be done by going to the SharePoint Central Administration > System Settings > Manage Farm Solutions, and then select the Nintex solutions you want to remove and click on "Retract Solution" then "Remove Solution"

Remove Nintex permission from user. Go to the SharePoint Central Administration > Security > Manage Permission Policy Levels and remove the Nintex permission level from the user policy.

Remove Nintex Configuration Database. After removing solutions and feature, the final step is to remove the Nintex Configuration Database from the SQL Server.

Please be aware that these steps can vary depending on the version of Nintex and your specific SharePoint Online environment, and that uninstalling a 3rd party app may have an impact on the other customizations and workflows on your SharePoint farm, so it's best to first test these steps on a test environment before proceed on production.