How can I return redirect action in application service?

I am writing a Application service, something like:

public class EventAppService : ApplicationService`enter code here`    
    public async Task<EventRegistrationDto> Register(RegisterInput input)
            {
                var @event = await _eventManager.FindByCodeAsync(input.EventCode);

                //TODO: change to abp session later
                var staff = await UserManager.GetUserByIdAsync(7);

                if (@event == null)
                    throw new UserFriendlyException(L("EventNotFound"));

                var eventReg = await _eventManager.FindRegistrationByCode(@event, input.AdmissionCode);            

                return ObjectMapper.Map<EventRegistrationDto>(eventReg);
            } }

After registered a new event, how can I return the redirect url ?