Among the data stored in splunk is in ipv6 format. I want to know how to convert the ipv6 format to the ipv4 format. In addition, ipv6 format to ipv4 format would like to know how to convert when reading know file.
IPv6 is a completely different addressing scheme than IPv4. You can't translate IPv6 addresses to IPv4 addresses.
The only thing I can think of is that you have IPv4 addresses in this notation: ::ffff:10.0.0.1. If that is the case, you can simply strip off the ::ffff: bit with whatever approach suits you.
Maybe I'm missing something, but then please explain a bit further what issue you have and what you want to achieve. Some sample data is always helpful for improving our understanding of your question.