Hi partner,
We will use the on-demand workflow and the "Bulk Workflow Execution" tool of XrmToolBox to update contacts in bulk.
First refer to these two documents to know how to create a workflow.
https://docs.microsoft.com/en-us/dynamics365/customerengagement/on-premises/customize/workflow-processes
https://crmbook.powerobjects.com/system-administration/processes/workflows/
Create such a workflow.
Check As an on-demand process, select Scope as Organization. Add Step: Update Record.

Select Update: Contact. Click Set Properties.
First select a value of two option set field, then at Form Assistant, select Originating Lead (Lead), then select lead's two option set field, then OK.

Activate this workflow.
If there are many existing contacts that need to be updated in your environment, then we need to use the "Bulk Workflow Execution" tool of XrmToolBox to update all contacts at once.
This is the download page for XrmToolBox: https://www.xrmtoolbox.com/
After downloading and unzipping it, open XrmToolBox.exe.
Install Bulk Workflow Execution in the tool library. Connect to your D365 organization.
With Bulk Workflow Execution open, select the workflow and the contact view. Click Validate Query first, and then click Start Workflows.
In this way, all contacts in this view will be updated according to the selected workflow.