Struggling with Organizational Development Diagnosis? Seeking Guidance on Where to Start

Hello Everyone, I am working as an HR professional in an educational institute. I have been assigned a project on organizational development. I am very confused about the diagnosis part. I am not getting a clear idea of how to start the diagnosis and what exactly I have to do. Can you please suggest the right process?

Thank you.

I need clarification on what you mean by diagnosis to help me come back to you.

Regards,
S.K. Johri