You can use your OS tools and utilities to identify resources in use and preventing unmount - e.g. if there is still some open file from your mount.
In some systems it can be command like lsof +f -- /path/to/local/mount. Read your OS documentation for details.
You can also try "lazy" fusermount option (check man pages for exact option as it can differ between different OS)
If above gentle ways fail you can force unmount e.g. on macOS by running diskutil unmount force /path/to/local/mount. This command is also OS specific...
Reboot will help too but should be really the last resort. It works on any OS:)