If you know the coordinates in the form of
chrom start stop (BED format) then you can use
samtools faidx (or
bedtools getfasta, search for those solutions here on Biostars) to retrieve the sequence you need from the genome sequence file.
samtools faidx reference.fasta samtools faidx reference.fasta chr_ID:1-108
You could also use a different genome (track) visualization software such as GenomeView or Artemis or such which are specifically developed of annotating and thus offer easy and efficient ways to add/remove and get sequences for certain genes. But can be launch form the web so not local install needed.