This is a tab-separated-value format file. There are many tools for working with .tsv files, but some (Excel is a prime example) will probably not work with such a file unless you split it into smaller pieces. A scripting language or the linux/unix command line utilities like grep and awk are probably necessary. For your problem, I would consider using grep to pull out lines in the original file that contain variants in your gene of interest. Then, use this subset of the file in Excel.