It’s in every image, buddy. Read the installation guide [Guide] S922X-J (Ugoos AM6b+) CoreELEC installation and FAQs - General / Guides & How-tos - CoreELEC Forums
It states very clearly where the dtb is located, where to place and name it:
Preparing Installation Drive
1. Connect the USB Storage to your PC and open Balena Etcher
2. Select the CoreELEC’s image file (eg. CoreELEC-Amlogic-ng.arm-21.0-Omega_nightly_20240430-Generic.img.gz)
3. Select the USB Storage that you want to use, proceed with the installation and make sure that it will complete successfully.
4. Open the COREELEC partition, navigate to “device_trees” folder
5. Copy the appropriate dtb file, e.g. g12b_s922x_ugoos_am6b.dtb file to the root of your COREELEC partition. Then, rename it dtb.img
6. Copy dovi.ko to the root of your COREELEC flash drive.
7. Copy remote.conf to the root of your COREELEC flash drive.
8. Safely remove the USB drive from your PC