How to manage employee as external candidate

Summary:

Hi,
our client would like to change the contract of an employee from fixed-term to open-ended by recruiting through the application for an external job requisition using the check duplicate that the system does not have at disposal in these cases.

What is the best practice we can suggest?

Is it correct to go through recruiting to carry out this change or do you have to perform the action from employment contracts?

Thanks

Regards

Francesca