use a query that returns all the records from the country table and a second query that returns all records of the person table and link them to datasources lets name them QryPerson for the person query DSPerson for the person datasource and QryCountry, DSCountry for the country controls respectively. DBLookupCombobox has 2 groups main groups of properties 1) the data to be changed when the combobox is used to select a value and 2) the query that provides the values you can choose from.
in the first group are the properties Datasource, Datafield which must be linked to the DSPerson and IDCountry field and in the second group are the properties Listsource linked to dsCountry, listField must be linked to the Country_name field and KeyField that must be linked to the DSCountry.ID field.
After that if you use the default property values every time you select a country in the dblookupcombobox it will change the active record's idcountry field value the new one selected. All filling and setting is taken care for you internally.