Heat it to 280 °C or higher (depending from the max. temperature of your column brand) for at least 30 min and purge with mobile phase. Inject solvent and heat again until the impurities disappear.

https://www.researchgate.net/post/Do_you_have_a_method_to_clean_a_GC_column

If heating will not work, you can rinse it with methanol.

regards,

GB

Usually cut 1-2 meteres of front end helps in reducing contamination. There are some kinds of backwards ellution with solvents but its tricky and not so much helpfull.

https://link.springer.com/content/pdf/bbm:978-3-642-54640-2/1.pdf

https://phenomenex.blob.core.windows.net/documents/2d812e27-959e-4914-93b1-049b4549b9fa.pdf

https://chemetrix.co.za/wp-content/uploads/2021/07/Enhance-Your-GC_MS-Productivity-and-Accuracy_-Agilent-GC_MS-columns-and-supplies.pdf

https://www.duratec.info/index.php?option=com_docman&task=doc_view&gid=36&Itemid=10&lang=de

Regards