post your project here, it would be better if we can see the whole project,
Probably you have made a naming-error of your user-module.Make sure, that your Amplifier is named "PGA" and not "PGA_1"
It looks like you have accepted the default name of PGA_1_...., so
last line of code should be changed from
PSoC Designer allows multiple instances of user module to placed in the design, if sufficient analog/digital blocks is available. Instance name of the user module includes a number which gets incremented everytime you place the module in the design. For example, the first time you place the PGA user module in the project, it will be named as PGA_1. The second time, it will be PGA_2 and so on.
In the firmware, to refer to particular instance of the user module, you should use appropriate name. To understand the code flow, you can refer the user module datasheet. But you should use the APIs given in header (.h) file to configure/use the particular instance of the user module. Note that .asm and .h file for a particular user module instance appends to the designer project (and can be seen in workspace), when you "generate" the project.