A first step can be disassembling and then decompiling the binary. A good, free tool for this is Ghidra: https://ghidra-sre.org/ https://ghidra-sre.org/ It wil

A first step can be disassembling and then decompiling the binary. A good, free tool for this is Ghidra: https://ghidra-sre.org/ https://ghidra-sre.org/ It will not give you code that you can recompile, but it should be possible to understand and recreate the code based on the result of decompiling the software An alternative approach can be to emulate the binary under e.g. qemu