I dont know if you found the Generate Config Button, but here's some guidelines on how to find it.
Make a PSTN Gateway with Audiocodecs 114 at the end of the configuration wizard, right after you add an outbound rule there will be a page full of links on how to setup gateways.
At the bottom of that page you will find the Generate Configuration button.
Now if you have found it and clicking doesnt do anything, i've never seen that case before, all i can suggest for you is that maybe you had some Uncleaned traces from a previous 3CX Installation which caused it.
If you cant be bothered to uninstall here's the configuration file which you will need to modify to suit your needs.
There are 2 Fields in which you will need to put your Machine's IP at.
Replace XXX.XXX.XXX.XXX on these 2 fields with your IP
LocalOAMIPAddress = XXX.XXX.XXX.XXX
ProxyIp 0 = XXX.XXX.XXX.XXX;