This project is based BetaFPV's project LiteOSD which in turn based on another project named DIY-OSD. Know more about DIY OSD on RCGroups. https://www.rcgroups.com/forums/showthread.php?1473207-Diy-osd-(Arduino-and-opensource)
Go to inc/config.h and comment/uncomment defines depending on what variant you need. Then import project to Silabs Simplicity Studio 5 and build it.
MCU: Silicon Lab EFM8BB21f16G_A_QFN20
IDE: uVision Keil (C51 Lab)