You can make use of HCM Data Loader to upload Succession Plans (Incumbent, Job and Position Types).
Use the below sample file to load Succession Plans:
METADATA|SuccessionPlan|PlanName|PlanType|Status|AccessTypeCode|Description|IncumbentPersonNumber|JobCode|JobSetCode|DepartmentName|DepartmentSetCode|GradeSetCode|GradeCode|PositionCode|BusinessUnitName|SourceSystemId|SourceSystemOwner
MERGE|SuccessionPlan|Test_Person_Succession_Plan|INCUMBENT|ACTIVE|PUBLIC|Sample description for Incument Plan Type.|111222|||||||||HRC_SQLLOADER_Test_Person_Succession_Plan_INCUMBENT|HRC_SQLLOADER
MERGE|SuccessionPlan|Test_Job_Succession_Plan|JOB|ACTIVE|PUBLIC|Sample description for Job Plan Type.||XX052|COMMON|Test HR Department|COMMON|COMMON|GRD_90||XX BU|HRC_SQLLOADER_Test_Job_Succession_Plan_JOB|HRC_SQLLOADER
MERGE|SuccessionPlan|Test_Position_Succession_Plan|POSITION|ACTIVE|PUBLIC|Sample description for Position Plan Type.||||Test HR Department|COMMON|||POS_0301|COMMON|HRC_SQLLOADER_Test_Position_Succession_Plan_POSITION|HRC_SQLLOADER
METADATA|SuccessionPlanOwner|PlanName|PlanOwnerPersonNumber|OwnerTypeCode|SourceSystemId|SourceSystemOwner
MERGE|SuccessionPlanOwner|Test_Person_Succession_Plan|99997|ADMINISTRATOR|HRC_SQLLOADER_ADMINISTRATOR_99997_Test_Person_Succession_Plan|HRC_SQLLOADER
MERGE|SuccessionPlanOwner|Test_Job_Succession_Plan|99997|ADMINISTRATOR|HRC_SQLLOADER_ADMINISTRATOR_99997_Test_Job_Succession_Plan|HRC_SQLLOADER
MERGE|SuccessionPlanOwner|Test_Position_Succession_Plan|99997|ADMINISTRATOR|HRC_SQLLOADER_ADMINISTRATOR_99997_Test_Position_Succession_Plan|HRC_SQLLOADER
MERGE|SuccessionPlanOwner|Test_Position_Succession_Plan|99998|ADMINISTRATOR|HRC_SQLLOADER_ADMINISTRATOR_99998_Test_Position_Succession_Plan|HRC_SQLLOADER
Once the data is loaded, you can run the query to check loaded plans in HRM_PLANS table.