Bluetooth communication, How can I take number from string?

I would like help,
considering that I am a beginner in programming / creating mobile applications, I would beg you to help me with my problem.

I wrote a program to receive and send numeric values in the C programming language. I can send via bluetooth two types of commands via
one is: SerialBT.println(String(Temp1));
the second is: SerialBT.println(“TEMP2=” + String(Temp2));
I don’t care what sending command I use given SerialBT.println(String(Temp1)); or SerialBT.println(“TEMP2=” + String(Temp2)); but I have a problem with how to receive and print data for temp1 and temp2 on my mobile phone.

I don’t know which blocks to use so please help

Thank you in advance