Fix SharePoint Search Issue

I'm looking for an expert to fix the SharePoint search functionality.

Current Issue:
- The search is not working at all.
- After upgrading to SharePoint 2016, the search stopped functioning.

Ideal skills and experience:
- Extensive experience with SharePoint 2016.
- Strong troubleshooting skills.
- Familiarity with SharePoint search configuration and indexing.

Please provide a detailed plan to resolve this issue.