Error from last 2 lectures

I’m having this error from 2 lectures. I’m trying to resolve but it just leads to some other error.
Please Help! I’m currently on lecture 39.

1>------ Build started: Project: BullCowGame, Configuration: Debug Win32 ------
1>BullCowGame.obj : error LNK2019: unresolved external symbol “public: __thiscall FBullCowGame::FBullCowGame(void)” (??0FBullCowGame@@QAE@XZ) referenced in function “void __cdecl `dynamic initializer for ‘BCGame’’(void)” (??__EBCGame@@YAXXZ)
1>C:\Users\HARSHIT SINGH\source\repos\Section_02\Debug\BullCowGame.exe : fatal error LNK1120: 1 unresolved externals
1>Done building project “BullCowGame.vcxproj” – FAILED.
========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========

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