The Center for Open Science has brought together a team to create a useful template for secondary data analysis preregistrations. Check it out here https://osf.io/x4gzt/ and cite:
Weston, S. J., Mellor, D. T., Bakker, M., Van den Akker, O., Campbell, L., Ritchie, S. J., … DeHaven, A. C. (2020, September 22). Secondary Data Preregistration. Retrieved from osf.io/x4gzt