Navigate to Salesforce's Appexchange
1. Install the Axsy Mobile App for Field Service Lightning on AppExchange. You will need to assign your users a licence for the Salesforce Field Service Powered by Axsy Managed Package.
2. Optionally, install Axsy Smart Forms on AppExchange. This package is free so licences will be assigned to all users. Please see here for more information: Smart Forms Portal
For more on how to navigate AppExchange, please see this Trailhead by Salesforce: Install AppExchange Packages