How To Convert Object to T

I Have a operator class that a func is on it, if argument of Function(it is a Func) was int or float or string i can convert object and call Func with "Function((T)a)", when T be a List how can i convert object a to T? (i know that T is List of Something)

using System;
using System.Collections;
using System.Collections.Generic;
using System.Linq;

namespace GameToolkit.Operator
{
    public abstract class IOperator
    {
        public abstract Type OutputType { get; }
        public abstract Type[] GetInputTypes();
        public abstract object GetValue(object a);
        public ValueToken GetValues(object a)
        {
            var v = GetValue(a);
            return new ValueToken() { Type = v.GetType(), Value = v };
        }
    }
    public class SingleOperand<T, O> : IOperator
    {
        public Func<T, O> Function { get; set; }
        public SingleOperand()
        {
        }
        public SingleOperand(Func<T, O> function)
        {
            Function = function;
        }
        public override object GetValue(object a)
        {
            if (Function == null)
                return default(T);
            if (a.GetType().IsGenericType)
            {
                ///SOME CODE HERE!!!
            }
            else
            return Function((T)a);
        }
        public override Type OutputType => typeof(O);

        public override Type[] GetInputTypes()
        {
            return new[] { typeof(T) };
        }
    }
}