  The nearby long-duration GRB 191019A recently detected by Swift lacks an
associated supernova and belongs to a host galaxy with little star formation
activity, suggesting that the origin of this burst is the result of a merger of
two compact objects with dynamical interactions in a high-density medium of an
active galactic nucleus. Given the potential motivation of this event, and
given that it occurs in such a high-density environment, the
ejecta-circumstellar medium (CSM) interaction cannot be ignored as possibly
contributing to the kilonova emission. Here, we theoretically calculate the
kilonova emission by considering the contribution of the ejecta-CSM interaction
in a high-density environment. We find that the contribution to the kilonova
emission from the ejecta-CSM interaction will dominate at a later time, and a
smaller ejecta mass will have a stronger kilonova emission from the ejecta-CSM
interaction. Moreover, we try to apply it to GRB 191019A, but we find that it
is difficult to identify the possible kilonova emission from the observations,
due to the contribution of the bright host galaxy. On the other hand, less
injected mass (less than $M_{\rm ej}=2\times10^{-5}M_{\odot}$) will be required
if one can detect the kilonova emission associated with a GRB 191019A-like
event in the future. The {\em r}-process-powered and spin energy contributions
from the magnetar are also discussed.
