just put the name or the path to your file in a .gitignore file, like this:
your_file.svg <-- ignore the file your_file.svg
*.sql <-- ignore any .sql files
ihm/test/ <-- ignore the whole "test" folder in "ihm"

# OSX
#
.DS_Store
# Xcode
#
build/
*.pbxuser
!default.pbxuser
*.mode1v3
!default.mode1v3
*.mode2v3
!default.mode2v3
*.perspectivev3
!default.perspectivev3
xcuserdata
*.xccheckout
*.moved-aside
DerivedData
*.hmap
*.ipa
*.xcuserstate
# Android/IntelliJ
#
build/
.idea
.gradle
local.properties
*.iml
*.hprof
# node.js
#
node_modules/
npm-debug.log
yarn-error.log
# BUCK
buck-out/
\.buckd/
*.keystore
!debug.keystore
# fastlane
#
# It is recommended to not store the screenshots in the git repo. Instead, use fastlane to re-generate the
# screenshots whenever they are needed.
# For more information about the recommended setup visit:
# https://docs.fastlane.tools/best-practices/source-control/
*/fastlane/report.xml
*/fastlane/Preview.html
*/fastlane/screenshots
# Bundle artifact
*.jsbundle
# CocoaPods
/ios/Pods/

git reset name_of_file