If you use the search capabilities of this site (the magnifying glass icon on the bar) and type in "4th axis" you will find lots of discussions of things of this nature, most having to do with post processors.
The problem with this type of question is that a post processor generally needs to be tailored for the specific machine. The motion commands of G-code are pretty much standard, but there are commands associated with non-motion G codes and M codes that are applicable to only your machine and controller.
There is usually a sequence of commands that need to be done before doing a tool change, for example. This will be specific to your control and machine manufacturer and can be very different from machine to machine.
With 4th axis machines, there is a question of how the 4th axis angles are specified for your controller. Are angles 0 to 360 degrees? -180 to 180 degrees? You need to know so you can tell the post what to output.
Any machine I've done a post for I've needed to have code examples that work on that machine so I can make the settings and do any other programming needed so I get outputs that are good.
As you'll find in the various other discussions here, Austin NC is often cited as a good source for post processors. You could contact them and see what they can do for you. If your machine is a common type, they might have already done a post for it.
