How do I call a method on an object from a DLL?

I understand how to call a method not encased in a class using offsets like this through DLL injection:

test.dll

#define TEST_FUNCTION_OFFSET    0x109010 // random offset

typedef __int64(__cdecl * _test)(void);
_test test;
DWORD WINAPI MainThread(LPVOID param) {
    std::uintptr_t base_address = reinterpret_cast<uintptr_t>(GetModuleHandle(NULL));
    test = (_test)(base_address + TEST_FUNCTION_OFFSET);
    test();
}

BOOL APIENTRY DllMain(HMODULE hModule, DWORD  ul_reason_for_call, LPVOID lpReserved) {
    switch (ul_reason_for_call) {
        case DLL_PROCESS_ATTACH:
            CreateThread(NULL, NULL, MainThread, hModule, NULL, NULL);
            break;
        case DLL_PROCESS_DETACH:
            break;
    } return TRUE;
}

main.cpp

#include <iostream>
#include "example.h"

void test() {
    std::cout << "Test" << std::endl;
}

int main() {
    example ex;
    ex.incrementID();
    return 0;
}

example.h

class example {
    private:
        int _id = 1234;
    public:
        void incrementID() { _id++; };
};

But how would I go about calling incrementID() on the ex object in main() if I have the addresses of example::incrementID() and ex?