A company has an external system that stores client accounting data but they want to...

Three steps that the administrator should take to implement this functionality are:

Create an External Data Sourcepointing to the external system’s database. An External Data Source is a type of metadata that defines the connection and authentication information for an external system that stores data outside of Salesforce. The administrator can create an External Data Source using the Lightning Connect OData 2.0 or 4.0 adapters, which support read-only access to data in relational databases.

Create an External Object for each table of accounting data in the external system. An External Object is a type of custom object that maps to a table in an external system. The administrator can create an External Object for each table of accounting data that they want to access from Salesforce, and define its fields and relationships accordingly.

Create an Indirect Lookup field to connect to the Account. An Indirect Lookup field is a type of custom field that links a child External Object record to a parent standard or custom object record. The administrator can create an Indirect Lookup field on the External Object that references the Account object, and specify the external column name and value that match the Account ID.

Verified References: https://help.salesforce.com/s/articleView?id=sf.external_object_overview.htm &type=5https://help.salesforce.com/s/articleView?id=sf.external_object_relationships.htm &type=5