This document will help you to record a new prompt on Asterisk, which can then be used for welcome IVRS messages.
For example, if you want a custom prompt like "Welcome to XYZ Company, please dial 1 for Sales support and please 2 for customer support"
In asterisk you first need to define a number where you will call up and record the prompt.
Also you would need a location to store that prompt
In extensions.conf please do the following
; Record voice file to /tmp directory
exten => 1111,1,Wait(2) ; Call 1111 to Record new Sound Files
exten => 1111,2,Record(/tmp/asterisk-recording:gsm) ; Press # to stop recording
exten => 1111,3,Wait(2)
exten => 1111,4,Playback(/tmp/asterisk-recording) ; Listen to your voice
exten => 1111,5,wait(2)
exten => 1111,6,Hangup
Dial the number 1111 and you will hear a beep, start recording the prompt and press # when you are finished.