I think that the best way to use KPI during ISO 9001 implementation is to start monitoring and measuring early and using KPI performance analysis and evaluation as raw material to determine relevant improvement opportunities. So, when starting to implement ISO 9001, determine processes and describe them as they are. Then, check if applicable ISO 9001 requirements are already in place. You start with a picture of processes “as is”. Then, based on KPI performance you focus your resources on what needs to be improved not based on opinion but on KPI performance feedback.
The following material will provide you more information:
Free webinar on demand - Measurement, analysis, and improvement according to ISO 9001:2015 - https://advisera.com/9001academy/webinar/measurement-analysis-and-improvement-according-to-iso-9001-2015-free-webinar-on-demand/.