You can see in Unacademy for Free lectures of UPSC Prelims & hopefully you will get quite a good number of videos available there. Also in youtube you can get some classes from Mayur Mogre on Current Affairs and Dristi IAS classes. But this may not be sufficient for your preparation and if you are serious then you have to work hard by yourself or have to join any coaching institute online or offline mode according to your convenience.

You can follow the UPSC preparation tips from career360 which will surely help in your preparation by just following the link:

https://competition.careers360.com/articles/how-prepare-for-upsc-ias#:~:text=IAS%20Exam%20Preparation%20Tip%203,Services%20Preliminary%20and%20Main%20examination.

I hope this answer helps. All the very best for your future endeavors!

You may refer to the numerous Free Study Material available on platforms like Clear IAS or Byjus for Prelims Preparation besides referring to Youtube Vidoes of Top Educators, following recommened books and revising Notes, syllabus wise. You may attempy Free Prelims Mock Tests available across Internet for UPSC and judge your Preparation. You may check Youtube Channel of Byjus IAS, you have free Crash Course Videos uploaded there, which help you revise the complete syllabus.

For more information about UPSC 2021 Preparation do follow the link below

https://competition.careers360.com/articles/how-prepare-for-upsc-ias