If you need to get in touch with the Service Provider about a job they accepted, your best bet is to use the in-app chat.
Click the "Calendar" icon to view your upcoming jobs.
Click the job in question.
Click "Chat" on the job page.
4. Type up your message to the Service Provider.
5. Tap "Send" (the paper plane icon.)
6. Make sure that you have your chat notifications on so you don't miss your Service Provider's response.