Hello Alex,

You could integrate it via API application. 

Another option could be just to export the orders from that site into .CSV file -if this is possible, and the import them into Linnworks via Open Order import. More information in regards this can be found here: https://www.linnworks.com/support/settings/import-and-export-data/import-data/import-types/order-import

I hope this helps.

Please, let me know if you have further questions.

Kind regards,

Angela