Please note that pointers are used instead of references: ...

int main(){

    std::vector<int> testData{100,500,60};
        
    auto atValue = [=](std::vector<int> &vec,int *data){
        for(auto it = vec.begin();it != vec.end();it++){
            if (*it == 500) {
                data = &*it;
                break;
            }
        }
    };
    
    
    int *tint = NULL;
    atValue(testData,tint);
    //*tint = 50;
    printf("%d",*tint);    
    
    return 0;
}

felix said:
int data changed to int &data

The problem has been solved.Thank you.