Finally, I am able to solve that issue.
do() is replaced by tap().
for reference https://www.academind.com/learn/javascript/rxjs-6-what-changed/
and tap() should be inside .pipe().
like this, .pipe(tap())
for more reference, you can refer this link,
https://alligator.io/angular/angular-6/
and
https://www.learnrxjs.io/operators/utility/do.html

http://bit.ly/31LeglK

import { of } from 'rxjs';
import { tap, map } from 'rxjs/operators';