Just use .retainAll { ... } or .removeAll { ... }, both accepting a predicate, to filter it in-place:
items.retainAll { shouldRetain(it) }
items.removeAll { shouldRemove(it) }
Note that items should be a MutableList<T> for that, not just List<T>, which is a read-only list in Kotlin and thus does not expose any mutating functions (see: Collections in the language reference).
By the way, these two function are implemented efficiently for lists that support random access: then the list is not compacted after each item is removed (O(n2) time worst-case), and instead the items are moved within the list as it is processed, giving O(n) time.
And if you don’t want to modify the original list, you can produce a separate collection with only the items you want to retain using .filter { ... } or .filterNot { ... }, this will work for read-only List<T> as well:
val filtered = items.filter { shouldRetain(it) }
val filtered = items.filterNot { shouldRemove(it) }