Hello @Nickkoro,
and welcome to KNIME Community!
Uninstalling KNIME requires to install extensions again (see bottom topic how to obtain list of installed extensions) but workflows you can simply export (File --> Export KNIME Workflow...) and then import once KNIME is installed again. Or you can copy entire workspace to another location and upon Windows reset bring it back. You can also export preferences (File --> Export Preferences...).
Check this topic:
If you have any questions don’t hesitate to ask 
Br,
Ivan