As you told I have changed "if(dimdim_is_teacher($dimdim))" to "if(dimdim_is_teacher($dimdim))" in "view.php" file available at "\moodle\moodle\mod\dimdim".
Now the problem is any instructor can start the meeting. ButI want to restrict only for that perticular instructor to start the class, who has created that class.
If you leave the "if(dimdim_is_teacher($dimdim))" as it is but change /db/access.php adding:
'mod/dimdim:manage' => array(
'captype' => 'write',
'contextlevel' => CONTEXT_MODULE,
'legacy' => array(
'teacher' => CAP_ALLOW,
'editingteacher' => CAP_ALLOW,
'admin' => CAP_ALLOW
and re-install the dimdim module. You will be able to control the access correctly through the moodle roles.