Here's the process that worked for me:
1) Download
https://www.iar.com/iar-embedded-workbench/ for ARM
2) Install the IAR software. WARNING: It requires registering and getting a temporary license from IAR. The software is not hobbyist focused. Poor decision on Geetech's part to use this tool. Hopefully the momentum picks back up to migrate to Eclipse.
3) Download the Geeetech Smartto-IAR source code
https://github.com/Geeetech3D/Smartto-IAR
4) Find the GTM32.eww file in the Project directory of the source code and open it.
5) In the workspaces section of the IDE, right above the source code project hierarchy, make sure you've chosen A30 from the dropdown menu
6)There are files missing from the source code that will prohibit it from compiling so you need to copy files from the IAR directory
Go to this location "C:\Program Files (x86)\IAR Systems\Embedded Workbench 8.2\arm\src\flashloader\NXP\FlashQN9080\chip_qn908x\cmsis (or wherever your IAR is installed) and copy all the files except the "core_cm0.h" file and paste them back into this folder wherever you downloaded the source code to: "...Smartto-IAR-master\src\STM32F10x_Core\"
7) Once those files have been copied to the source code location, you should be able to right click on the project and select Make and it will compile. You should have a number of warnings, but no error messages. You can ignore the warnings.
8)All changes you need to make should be made in the "Configuration_GTM32_Pro_A30S.h" file which is under the User directory. It has many of the same settings as Marlin 1.1.x
If you get it to compile and need assistance in uploading it to the machine, i can share how i did that also.
Lastly, keep in mind that if you are using a BLTouch, this version of the source code is not going to work. It does work for the proximity sensor however.