Call web service in site workflow to start list workflow on list

Create site workflow that will call the list workflow on each item that meets the specific criteria. The site workflow should start the SurveyReminder list workflow for each item where WeekAfterReminder = Not Sent I will need documentation regarding how the method is selected after selecting the web service to use. Also, I'll need to know how the web services and method locations are found and what's different between web services in Office 365 (SharePoint Online) and SharePoint 2013 On-Prem. Document Library Name: Books Columns in Library: WeekAfterReminderSent (choice): Not Sent (default); Sent RequestorName (person or group) SupplierName (single line of text) Name (single line of text) Date Required (date & time) List workflow attached to Books library: SurveyReminder SurveyReminder workflow will send an email with a detailed description (I can handle this part)