A few options are listed below with some outside resources if valuable.
git config --global difftool.bc.path "c:/program files/beyond compare 4/bcomp.exe"
git config --global mergetool.bc.path "c:/program files/beyond compare 4/bcomp.exe"
Configuring Beyond Compare with Git
git config --global --add merge.tool kdiff3
git config --global --add mergetool.kdiff3.path "C:/Program Files/KDiff3/kdiff3.exe"
git config --global --add mergetool.kdiff3.trustExitCode false
git config --global --add diff.guitool kdiff3
git config --global --add difftool.kdiff3.path "C:/Program Files/KDiff3/kdiff3.exe"
git config --global --add difftool.kdiff3.trustExitCode false
or in Config file
[merge]
tool = kdiff3
[mergetool "kdiff3"]
path = C:/Program Files/KDiff3/kdiff3.exe
trustExitCode = false
[diff]
guitool = kdiff3
[difftool "kdiff3"]
path = C:/Program Files/KDiff3/kdiff3.exe
trustExitCode = false