How to cast PropertyInfo value to ICollection

I'm building my own generic solution to Entity Framework update in disconnected scenario. Many different approaches could be taken but I decided to decorate ICollection properties inside my entities with a custom attribute so that I can check the state of each entity inside those collections. Here's a sample entity with a navigation property:

public class{
   public int TaskId{get;set;}
   public string Instruction {get;set;}
   [EntityNavigationProperty]
   public virtual ICollection<TaskExecutor> Executors {get;set;}
}

public class{
   public int TaskExecutorId{get;set;}
   public int TaskId{get;set;}
   public virtual Task Task{get;set;}
}

public class EntityNavigationProperty:Attribute{}

I have a generic Update method that I'm planning to use to update any type of entity which will ensure that the related entities also get updated properly.

1 public void Update (TEntity entity){
2   PropertyInfo[] properties=entity.GetType().GetProperties();
3  foreach (PropertyInfo pi in properties)
4  {
5     if(Attribute.IsDefined(pi,typeof(EntityCollectionPropertyAttribute))){
6        foreach (//here I need to iterate through the ICollection object){
7               
8                   
9        }
10      }
11    }
12}

Now, assume I'm sending an instnce of Task to the above update method.In line 3, when iterator comes to the Executors property, the condition in line 5 resolves to true. Now I need to iterate through the Executors property and do appropriate tasks. For this particular case, in line 6 I can say:

  foreach (var item in (pi.GetValue(entity) as ICollection<TaskExecutor>))

But how can I determine what to type instead of T in ICollection?