RxJava library functions import issue

[TaraAndroid]

I have downloaded project. It gives me Rx java import issues all over the project. Do I need to implement rx java library in project?
below are few import issues listed
error: package rx.functions does not exist
import rx.functions.Action1;

import rx.Observable;
import rx.Subscription;
import rx.functions.Action1;
import rx.subscriptions.CompositeSubscription;

etc.

I have implemented "implementation 'io.reactivex.rxjava2:rxjava:2.2.7'" . even though does not works. Please suggest what to do.