Create a bootable SD card using the AMLGX "box" image, then edit the uEnv.ini file in the root folder of the SD card and change @@DTB_NAME@@ to meson-gxbb-wetek-hub.dtb or meson-gxbb-wetek-play2.dtb then save/eject and boot the box using the SD card. If you have been booting from SD card before it should automatically detect the card and boot into LibreELEC. If you have been booting from eMMC you may need to select "boot from SD Card" during boot.
Once the box has booted into the "box" image you can download the latest WeTek "board" image and install LibreELEC to internal eMMC storage using emmctool. This permanently overwrites the Android vendor OS with LibreELEC.
Find the URL for the relevant board image on the download page. For example, the LibreELEC v11 beta 1 image for the WeTek Play2 will be:
emmctool w LibreELEC-AMLGX.arm-11.0.0-wetek-play2.img.gz
The emmctool utility will write the board image to eMMC, expand the /storage partition to 100% size and change the partition labels to BOOT and DISK to avoid clashing with the default labels used in the SD card image (so you can boot from SD card if needed).
Once emmctool has finished, run shutdown and remove the SD card. Then cycle power to boot into LibreELEC running from the internal storage.