Based on your query, I believe, you need support on how to remove a control that you already added to the page. As per your code you are adding the controls using the method
this.Controls.Add(textadd1);
To remove the controls you have three methods, Remove, RemoveAt and RemoveByKey. see the corresponding documenation links below.
Remove - https://learn.microsoft.com/en-us/dotnet/api/system.windows.forms.control.controlcollection.remove?view=windowsdesktop-6.0
RemoveAt - https://learn.microsoft.com/en-us/dotnet/api/system.windows.forms.control.controlcollection.removeat?view=windowsdesktop-6.0
RemoveByKey - https://learn.microsoft.com/en-us/dotnet/api/system.windows.forms.control.controlcollection.removebykey?view=windowsdesktop-6.0
basically, you may use below. Make sure the variable index contains the index of the control to be deleted.
this.Controls.RemoveAt(index)
Hope this helps