Delete the Tvheadend42 addon folder in the .kodi/addons folder and in the userdata/addons folder. Do the same for the tvh.pvr folders.
Reboot.
Reinstall both from the Coreelec repository.
Unfortunately this will mean that you will have to rescan your sats and reconfigure your channels.
The version of Tvheadend changed in some fundamental way between these builds and having any carry over of the data or setting will likely prevent the addon from launching. i had similar issues with my migration and when I tried copying over my old Tvheadend42 folder from 8.90.2 it prevented the service from launching. However after clearing out the old and reinstalling the new everything worked again.
Shoog