MD Redirect Canonical Fix is a plugin that fixes two WordPress tickets (#41891 and #43274) that are still not fixed in WordPress core. It is meant to be used as companion plugin with Change Core Slugs plugin in cases where you set page or comments-page bases to include any non-ASCII character, or when feed or comments bases are set.
When these two bugs are fixed, you will not need this temporary plugin. There is a built-in mechanism that checks this repository whether plugin is not needed anymore. It also checks if there are newer versions of this plugin that you must manually install.
If you already have installed plugin MD Redirect Canonical Fix, you must deactivate it first, then delete it through Plugins screen. After that, you should download latest version from Releases page, and upload it through Add New Plugin screen. Finally, you can activate it like any other plugin.