The best practice if your task has a manager/supervisor on-site and you have already started working is to talk to them and explain what is going on. If you can't find the manager/supervisor, but they are on-site, then you can use the in-app chat feature to let them know what is going on or refer to your task materials to see how to contact the manager.
If you have not started working yet, please follow the directions in this article: I Can’t Make It To My Scheduled Task