Please refer to the section "How to add new app component in Flexbuild" in LSDK 20.04 user manual.
You could run the following commands and refer to ovs_dpdk and pktgen_dpdk source code in packages/apps/networking/.
$ flex-builder -c ovs_dpdk -a arm64
$ flex-builder -c pktgen_dpdk -a arm64
Then refer to sections "ovs_dpdk" and "pktgen_dpdk" in packages/apps/networking/networking.mk to create the building procedure.