Thanks for the answer,
I did the changes you said but the program gave me an error. Here is the error message:
Arduino: 1.8.14 Hourly Build 2020/12/04 05:33 (Windows 10), Board: "LOLIN(WEMOS) D1 R2 & mini, 80 MHz, Flash, Legacy (new can return nullptr), All SSL ciphers (most compatible), 4MB (FS:2MB OTA:~1019KB), v2 Lower Memory, Disabled, None, Only Sketch, 921600"
c:/users/burak_2022/appdata/local/arduino15/packages/esp8266/tools/xtensa-lx106-elf-gcc/2.5.0-4-b40a506/bin/../lib/gcc/xtensa-lx106-elf/4.8.2/../../../../xtensa-lx106-elf/bin/ld.exe: libraries\firebase-arduino-master\FirebaseHttpClient_Esp8266.cpp.o: in function `FirebaseHttpClientEsp8266::setReuseConnection(bool)':
C:\Users\Burak_2022\Documents\Arduino\libraries\firebase-arduino-master\src/FirebaseHttpClient_Esp8266.cpp:44: undefined reference to `kFirebaseFingerprint'
collect2.exe: error: ld returned 1 exit status
exit status 1
Error compiling for board LOLIN(WEMOS) D1 R2 & mini.
This report would have more information with
"Show verbose output during compilation"
option enabled in File -> Preferences.