How to sync a entity backed record when data changes in another system?

Hi

We have a data sync enabled Record which uses Database Table as a source. When any data gets updated in the legacy system, We need to sync the updated data in our record. To sync the changed record, in Appian documentation they have suggested to create a web api which includes a!syncRecords() function.
1. I wanted know by using a!syncRecords() whether API can sync the changed data by itself? if so, how it will typecast the data into Appian structure?
2. If it is not possible, how we can get the updated data and sync the record ?

Thanks