/m/ assimilates to /t/ and is realized as /n/.
/ë/ preceding /n/ is raised to /i/.
The form as inflected for third person conjunct is taken as a new base to which new suffixes are added.
/ë/ is inserted as a transition sound between /m/ and /n/.
Note: the root is derived from /kish-/ "finish" + /ëlënam/ "do."