Renumber Second Branch

Whats the syntax for renumbering the second branch only??

example, its currently {1;2} would be {1;0}

gets turned into

Renumber Second (13.1 KB)
thanks in advance.

Renumber Second (14.6 KB)

thanks!! thats pretty much what i ended up doing – when i posted i was having a bit of brain fog.

Would still like to see a path mapper solution if it’s possible.