Changing name by FixExpression

[Felipo17]

I have specific situation when tabels in my model are named like this: [0] Calendar, [1] Products, [EF] EquipmentFailure, etc (anything can be inside of square brackets). I made rule that checks if table name starts with "[" and if yes it suggest it to change. Now I want to apply a change that my Tables will be named like this: 0_Calendar, 1_Products, EF_EquipmentFailure and I want to make some FixExpression to do it automatically. Right now my JSON rule looks like this:
{
"ID": "AVOID_SQUARE_BRACKETS_AT_THE_BEGINNING_OF_TABLE_NAMES",
"Name": "Avoid square brackets at the beginning of table names",
"Category": "Naming Conventions",
"Description": "Table names should not start with a square bracket (e.g [1] Sales). Consider renaming to avoid compability issues or confusion.",
"Severity": 2,
"Scope": "Table, CalculatedTable",
"Expression": "Name.StartsWith("[") and Name.IndexOf("]") > 1 and Columns.Count > 1",
"FixExpression": "ObjectName = ObjectName.Substring(1, ObjectName.IndexOf("]") - 1) + "_" + ObjectName.Substring(ObjectName.IndexOf("]") + 2)",
"CompatibilityLevel": 1200
},
but it gave me errors :

• error CS1061: The type TabularEditor.TOMWrapper.Table does not contain a definition for ObjectName, and no accessible extension method ObjectName accepting a first argument of type TabularEditor.TOMWrapper.Table could be found.
• error CS0103: The name ObjectName does not exist in the current context.
  And I don't really know if there is any solution that can change my problem