Central doesn't have a native KML export. If you can share more about why you need a KML and what downstream system this KML will be used in, we might be able to suggest alternative approaches.
It's not a solution to export ODK Central geo data into KML, but there are techniques where, in a pinch, you can calculate KML within your original form from existing acquired geopoint/geotrace/geoshape questions; see ODK geoshape/geotrace/geopoint to KML
I am working with @Shridhar_Patel in the project of geo-spatial data analysis. KML format is required to us because we are collection polygon based data from various fields having agricultural phenomic data. That would ultimately used in the final analysis along with space data. Therefore, the field data accuracy would matter a lot and for that, our analysts use to verify each field (polygon) in Google Earth platform and convert it into shape file for geo-spatial data analysis. Further, as you may aware that these ground truth CSV files are not be directly used in satellite image processing softwares.
So, it would be appreciated if you could provide a sustainable and easy solution for the same.