You are missing a file from an add-on, most likely Solspace Calendar. You will need to verify the installation of that add-on is complete, and correct for your version of EE (which is either 3 or 4). The missing file would be
The other option is to remove the add-on, but this can be dicey if you already have an incomplete installation. To manually remove it, you'll need to go through several database tables (at least
exp_fieldtypes, and maybe even others) and remove reference to it. If you have the calendar field as an actual field in any channel, this gets even more complex to remove properly.
So go with the first option of verifying the installation and proceeding from there.