I can to put declaration String params; into Setup block
That won't do any good. You can leave the declaration of params where it is, but change the type to char * (may actually need to be const char *).
Get rid of the substring method call.
Change all the statements like:
if (params=="JvcPower") RemoteJVC(JVC_Power);
to
if (strcmp(params, "JvcPower") == 0) RemoteJVC(JVC_Power);
but I don`t understand about looking by Serial.print, looking for what?
If you put:
Serial.begin(115200);
Serial.println("Hey, I just reset...");
in setup(), and open the Serial Monitor, you should see:
Hey, I just reset...
If you see;
Hey, I just reset...
Hey, I just reset...
Hey, I just reset...
Hey, I just reset...
Hey, I just reset...
Hey, I just reset...
Hey, I just reset...
Hey, I just reset...
that is not good.