I've made the same mistake doing some testing. To fix it I wrote a small console app to list the user custom actions and pick and choose to delete them. Maybe for future reference:
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using Microsoft.SharePoint.Client;
using System.Security;
namespace SharePointCustomAction
{
class Program
{
static void Main(string[] args)
{
Console.WriteLine("Password:");
var password = GetConsoleSecurePassword();
Console.WriteLine();
using (var ctx = new ClientContext("https://tenant.sharepoint.com"))
{
ctx.Credentials = new SharePointOnlineCredentials("user@tenant.onmicrosoft.com", password);
var uca = ctx.Web.UserCustomActions;
ctx.Load(uca);
ctx.ExecuteQuery();
for (var i = uca.Count - 1; i > -1; i--)
{
Console.WriteLine(string.Format("Delete embedded script: {0}", uca[i].Title));
var input = Console.ReadKey();
if (input.KeyChar == 'y')
{
uca[i].DeleteObject();
}
Console.WriteLine();
}
ctx.ExecuteQuery();
Console.WriteLine("-----Finished------");
Console.ReadLine();
}
}
private static SecureString GetConsoleSecurePassword()
{
SecureString pwd = new SecureString();
while (true)
{
ConsoleKeyInfo i = Console.ReadKey(true);
if (i.Key == ConsoleKey.Enter)
{
break;
}
else if (i.Key == ConsoleKey.Backspace)
{
pwd.RemoveAt(pwd.Length - 1);
Console.Write("\b \b");
}
else
{
pwd.AppendChar(i.KeyChar);
Console.Write("*");
}
}
return pwd;
}
}
}
