Epson 3865X Plus - Manual (Page 191)

When you are going to use the application program, you need to
load the new mouse driver into the computer’s memory. You
can do this by just typing the name of the new mouse driver at
the MS-DOS command prompt, or you can modify your
AUTOEXEC.BAT file (or another batch file) to include the
name of the driver.
the
If you have included the file MOUSE.SYS in your
CONFIG.SYS file, you can use the same procedure above to
patch the .SYS file. Just substitute .SYS for .COM.
A-46 Using the VGA Utilities