How to add code to the HardwareSerial.h library ?...

Hello to everything. I could not add 3 lines of code in the HardwareSerial.h library and for this reason I could not load the code in the arduino
I appreciate everyone’s help

What board are you compiler for? If you choose Uno in the IDE, there is no register 'DDRA' but if you choose Arduino Mega, there is.

Please do not post pictures of code. Copy the text and post it here in code tags

Those look like member functions. Did you put them in the 'public:' part of the HardwareSerial object declaration?