How does one find the corresponding SNPs in the pair of chromonosmes in a FASTA file?
If you are looking for simple one off queries it might be better to load the BAM file and a relevant reference genome into a browser like IGV and simply navigate to that specific position.

For some data I had lying around a heterozygous SNP would look like the picture below, there has been an A to G SNP and a C to T:

For longer lists of queries I would take a look at BEDtools: https://bedtools.readthedocs.org/en/latest/content/bedtools-suite.html

If this does not help you, I recommend you ask your question on https://www.biostars.org/ There you will find help from true bioinformaticians.