Who is authorized to sign signature block I of the CDRL form. Is there an instruction on who completes and the approval process?
The approving authority is approving the decision to request the delivery of specified data based on need. That is either the program or project manager or the program or project data manager, not the contracting officer. The contracting officer will not know anything about data needs.
DD Form 1423 are provide in appendix B, paragraph 20.1 and figure 14 of MIL-STD-1388-2B
See DoD 5010.12-M, Chapter 3 Acquisition of Data for information on the establishment of data requirements.