Call a method inside SignalR Hub in Web api Core C#

Question

I use signalR hub to send messages and files in my web API service chat. I write a method to handle how messages send to clients as broadcast, user, or group :

public class MessageHub : Hub<IMessageHub>,IMessage
    {
        private readonly static ConnectionMapping<string> _connections = new ConnectionMapping<string>();
        private readonly static GroupMapping<string> _groups = new GroupMapping<string>();


        public async Task MessageDispatcher(ChatMessage message)
        {
            message.User = GetUserName();
            // Broadcast message
            if (string.IsNullOrEmpty(message.SendToGroup) && string.IsNullOrEmpty(message.SendDirectToUser))
                await Clients.AllExcept(Context.ConnectionId).SendMessage(message);//send all except current user
            //Send direct to user
            if (!string.IsNullOrEmpty(message.SendDirectToUser))
            {
                var connectionIds = _connections.GetConnections(message.SendDirectToUser);
                foreach (string userConnectionId in connectionIds)
                {
                    await Clients.Client(userConnectionId).SendMessage(message);
                }
            }
            //Send to group
            if (!string.IsNullOrEmpty(message.SendToGroup))
            {
                foreach (var user in _groups.GetUsers(message.SendToGroup))
                {
                    var connectionIds = _connections.GetConnections(user);
                    foreach (string userConnectionId in connectionIds)
                    {
                        await Groups.AddToGroupAsync(userConnectionId, message.SendToGroup);
                    }
                }
                await Clients.GroupExcept(message.SendToGroup, Context.ConnectionId).SendMessage(message);
            }
        }
}

Now I add a controller to my web API app to transfer files between clients because SignalR doesn't support file transfer as I found.

I want to call my MessageDispacher method to notify another user as my client wants but I don't have access to MessageDispacher.

any solution?