Hi,
If you'd like to create contacts for the existing leads conveniently, you can create an on-demand workflow targeting at Lead entity to achieve it.

Insert a step to create the related contact for the record.

Set the value of the field in contact record with the existing value which you need in the lead record.


Then update the lead record itself.

Set the contact just created as the parent contact of the lead.

After activating the workflow, you can select multiple / all leads and trigger the workflow for them manually.

It eliminates the challenge of having to create contacts for a large number of leads.
