You can find the guide in the download area.
Assuming you know the basic of preparing build environment...
- TWRP Source:
repo init --depth=1 -u https://github.com/minimal-manifest-twrp/platform_manifest_twrp_aosp.git -b twrp-12.1
sed -i '/<remove-project name="platform\/external\/gflags" \/>/d' .repo/manifests/remove-minimal.xml
repo sync -j$(nproc --all) --force-sync
- Device Tree (Make sure you are in root directory of TWRP source.):
git clone https://github.com/ratatouille100/twrp_device_samsung_a56x -b dev ./device/samsung/a56x
- Build (Make sure you are in root directory of TWRP source.)
source build/envsetup.sh; export ALLOW_MISSING_DEPENDENCIES=true; lunch twrp_a56x-eng; mka vendorbootimage
- Check
vendor_boot.imgin $OUT directory.