Thanks sir, one problem solved 
String s1 = receivedString[0]; // this line should get the sensor 1 value but idk which index
String s2 = receivedString[2]; // this line should get the sensor 2 value but idk which index
String s3 = receivedString[4]; // this line should get the sensor 3 value but idk which index
but how do i empty "receivedString" array when serial received the end marker?, i tried using the same line with "receivedChar" but it doesn't work.
i think its fine not to empty it since it reset the index to 0, but just in case.
and how do i identify which data i want it "receivedString" array?, the code above is just a guess.