Found a way for a newbie like you to build the fortran file.
Use libopenblas.a from
https://sourceforge.net/projects/openblas/files/v0.3.7/Download OpenBLAS-0.3.7-x64.zip
Tim S.
-------------- Build: Debug in blas_test (compiler: GNU Fortran Compiler)---------------
x86_64-w64-mingw32-gfortran.exe -Jobj\Debug\ -ffree-form -Wall -g -c C:\SourceCode\test\blas_test\main.f90 -o obj\Debug\main.o
x86_64-w64-mingw32-gfortran.exe -L..\blas_test -o bin\Debug\blas_test.exe obj\Debug\main.o -lopenblas
Output file is bin\Debug\blas_test.exe with size 16.58 MB
Process terminated with status 0 (0 minute(s), 3 second(s))
0 error(s), 0 warning(s) (0 minute(s), 3 second(s))