builtin_atxfer change

good day

asterisk 1.8.5.0
i want change how working builtin_atxfer function.
after part B ended call (hungup) do not connect part A and part C, but return both to default context.
how i can do this? what functions can i use?
code of asterisk is wery good with comments, but lot of functions :frowning:
please, help

To stand much chance of an answer, you need to use the developer mailing list or IRC channel. Even then, I suspect you may be asking for more work than most people are prepared to give for free.