Call async task method from another class using wpf/C# [duplicate]

I'm trying to call an async Task method, from another class. The method is place within a service I have created.

Service:

public class GetRoomsService
{
    public async Task<ObservableCollection<Room>> SearchForAvailableRooms(DateTime from, DateTime to)
    {
        ObservableCollection<Room> data = new ObservableCollection<Room>();
        return data; 
    }
}

In my wpf viewModel where I need to make the call, I have done it like:

// Start a search with default values from searchModel
RoomsList = _getRoomsService.SearchForAvailableRooms(searchModel.From, searchModel.To);

Where _getRoomsService in an instants of the service class. Now I need to call it when it's set to async Task

Have tried with:

RoomsList = Task.Run<ICollection<Room>>(() => { return _getRoomsService.SearchForAvailableRooms(Search.To, Search.From); }).Result;   

This does not work, and gives me an "Cannot convert lambda expression to delegate type" error.

Hope someone can see what I'm doing wrong.