iOS app for exporting HomeKit data?
I've been able to solve this as follows:


use iTunes to sync from iOS to Mac to create unencrypted iPhone backup
obtain and start iPhone Backup Extractor for OS X
select latest backup, then Expert Mode, then Application Domains, then com.elgato.eve, Documents, Elgato Systems##EveWeather##*sql (* stands for what looks like a device serial number) and extract SQL file to ~/Desktop/
sqlite3 ~/Desktop/Application\ Domains/com.elgato.eve/Documents/Elgato Systems##EveWeather##*sql reveals that the database contains 3 tables, one for humidity, temperature, and air pressure each
export tables e.g. to CSV files, then import e.g. into Excel