Anyone know how to update the Hobbywing Program Box?

Depends on which program box you're talking about, but generally you plug it into a computer and use the Hobbywing USB Link software to update the firmware.

Only the LCD programming box can be updated, the LED programming card can not. From the Hobbywing USB link software, select LCD program box from the Device menu.

Convinced a friend to buy a HobbyWing XR8 Pro ESC/motor combo recently as I've had the XR8 Plus for the last year with good results and figured the Pro is the same or better than the Plus. Told him that if he got it, I could enable reverse for him with my program card that I purchased new in January 2021 (Hobbywing Multifunction LCD Program Box, part #: 30502000014). He buys the ESC, and we're at the track yesterday and I connect to it but it says it needs a software update. Should this work to enable programing the XR8 Pro? I'm hoping so as I have an XR8 Pro combo new in box that I've been procrastinating swapping in.

I don't know that ESC but yes, it is common for the Hobbywing program box to require a software/firmware update to work with new ESCs.

https://www.hobbywing.com/article.php?id=162 contains the version history.