I moved into an apartment, with a dishwasher from a gentile. It has a plastic liner.
How would it be possible to use, without disposing of it.
It can be kashered by first ensuring that it is entirely clean, including spilling bleach or similar cleaning substance into cracks and crevices that might not be reached by water. The dishwasher should then be activated at maximal heat, for a full cycle.
Sources: According to most authorities, one can do hag’alah for plastic (see Iggros Moshe 2:92; Chelkas Yaakov 2:160). In addition, the dishwasher is usually used with substances that are pagum, and therefore the initial belios are not clearly issur. See also Mibeis Levi (Nissan 5756, p. 36), who writes that the dishwasher should not be kashered for Pesach, yet hints that this can in principle be done. In this case, where not kashering will involve a significant loss, one can be lenient, by means of the procedure above.