I found the solution.
First, create a file inputs.conf if it doesn't exist in /opt/splunk/etc/apps/Splunk_CiscoFirewalls/local/[inputs.conf]
Set into the file
[monitor:///path_to_the_directory_to_be_monitored]
disabled = false
sourcetype = cisco_asa
index = main
In Splunk, go to settings, data inputs, Add data. Next, click on "A file or directory of files" and click "Next"
Select "Skip preview", write the same full path than in the inputs.conf file. Let the source type on Automatic and the index on main.
Wait to the data to be indexed
Think to add fields (src/dst ip etc... in the left pan) in the search app
Regards,
... View more