How to load custom object records from one sandbox org to another in Salesforce?

It's necessary to setup and configure required metadata and users in your new or target org before beginning. You can migrate data by importing or inserting records from another Salesforce legacy source organization or other external source into a new target organization. It's important to import object data in a particular order to maintain record relationships.Record relationships are defined with Unique Record ID in Salesforce (and not record names) so you will need to match and replace old record Ids in your import files with the newly created data's record Ids from within your target org to properly prepare relational data for import.