There are several online study materials, videos, and tutorials available to help you prepare for the Prelims syllabus of the IBPS RRB PO Exam. Here are some reliable and comprehensive resources you can use:

1. EduRev:
EduRev is a trusted online platform that provides extensive study materials, video lectures, and practice questions for various competitive exams, including the IBPS RRB PO Exam. You can access their website to find a wide range of resources specifically designed to cover the Prelims syllabus.

2. YouTube Channels:
There are numerous YouTube channels that offer free video tutorials and lectures for banking exams. Some popular channels include:

- Bankers Way: This channel provides in-depth explanations of important topics, shortcut techniques, and mock tests.
- Adda247: Adda247 offers a wide range of videos covering different subjects, including reasoning, quantitative aptitude, and English.
- Study IQ Education: Study IQ Education offers comprehensive video lectures on various topics, including banking awareness and current affairs.

3. Online Coaching Platforms:
Various online coaching platforms provide structured courses and study materials for the IBPS RRB PO Exam. These platforms often include video lectures, study notes, mock tests, and doubt-solving sessions. Some popular online coaching platforms are:

- Gradeup: Gradeup provides comprehensive courses covering all subjects, along with video lectures and practice questions.
- Oliveboard: Oliveboard offers video courses, live classes, and practice tests for the IBPS RRB PO Exam.
- Testbook: Testbook provides video lessons, practice questions, and mock tests to help you prepare for the exam effectively.

4. Online Study Forums and Groups:
Joining online study forums and groups can be beneficial as it allows you to interact with fellow aspirants and exchange study materials and strategies. Some popular platforms for this purpose include:

- Bankers Adda: Bankers Adda has an active community of banking exam aspirants where you can find study materials and engage in discussions.
- IBPS RRB PO Exam Preparation Group on Facebook: This Facebook group is dedicated to IBPS RRB PO Exam preparation and provides a platform for aspirants to share resources and discuss important topics.

Remember to utilize these online resources effectively by creating a study plan, practicing regularly, and tracking your progress to ensure a successful preparation for the IBPS RRB PO Exam Prelims.