How do I replace the water supply shut off handle on this pcb pipe?

What would be the simplest way to replace it? I just want to replace the one handle since it snapped when I shut it off to replace the faucet. 🙃

I know pcb is bad and hasn’t been used in ages, but I inherited this place and the list of things that need replacing is mind boggling.

All the lines need to be replaced throughout the house and I’m looking into how to update them and bring everything up to code. For now…. Just the handle.