A tool created for InterPlot cannot be removed from MicroStation's interface. The tool is not found in the dgnlib custom tools are stored in, nor are any *.m01 files found on the computer, yet the tool remains in its toolbox on the MicroStation interface.
The iplot configuration file (iplot.cfg) can usually be found at C:\ProgramData\Bentley\InterPlot\iplot.cfg. Within this configuration file, there are several iplot-related configuration variables and coding. Find the configuration variable IPLOT_DLOG_SHOW_ICON which has the following description:
# IPLOT_DLOG_SHOW_ICON controls the disposition of IPLOT's toolbox. When set# to true, IPLOT will display a dockable toolbox when IPLOT's main dialog box# is loaded the first time. This toolbox remains displayed as long as IPLOT# is loaded in MicroStation. The toolbox contains a button which can be used# to invoke the dialog interface after it has been dismissed. When set to# false, no toolbox is displayed. The default value is false.
If IPLOT_DLOG_SHOW_ICON is set to true, replace the word true with false. Then, save and close the configuration file, reopen MicroStation and check that the tool and its toolbox are now gone.