@Jiri_Bam from your other posts I believe the sketch below is your regular BH1750 code and you want to make it work with Blynk, right?
I notice you tried to use @Dave1829's battery operated sensor code but you were struggling with an old IDE and some of the libraries. Unless you know the Blynk basics and have an identical set up to Dave you are going to struggle.
When I asked if you had tried any of the basic Blynk examples I was referring to simply controlling an LED etc before you move on to the BH1750.
int BH1750address = 0x23; //i2c address
int BH1750_Read(int address) //
buff[i] = Wire.read(); // receive one byte
void BH1750_Init(int address)
Wire.write(0x10);//1lx reolution 120ms
Suggest you search the forum for "Blynkify" and read all threads from start to finish that use this term.
If you are still struggling after you have done this let us know.