Finding previous year's question papers or mock tests that align with the Prelims syllabus for the IBPS RRB PO Exam can be a helpful way to prepare for the exam. These papers and tests provide an opportunity to familiarize oneself with the exam pattern, question types, and time management skills required to excel in the actual exam. Here's how you can find such resources:

1. Official IBPS Website:
- The official website of IBPS (Institute of Banking Personnel Selection) is a reliable source to find previous year's question papers and mock tests for the IBPS RRB PO Exam.
- Visit the IBPS website and navigate to the "CWE RRB" section.
- Look for the "Previous Year Question Papers" or "Model Papers" link.
- Download the available question papers and mock tests in PDF format.

2. EduRev:
- EduRev is a comprehensive platform that offers a wide range of educational resources, including previous year's question papers and mock tests for various exams, including the IBPS RRB PO Exam.
- Visit the EduRev website and search for "IBPS RRB PO Exam" in the search bar.
- Explore the available resources, including question papers and mock tests.
- Download or access the desired resources as per your preference.

3. Online Forums and Communities:
- Joining online forums and communities dedicated to banking exams can be a valuable resource to find and share previous year's question papers and mock tests.
- Participate in discussions and ask fellow aspirants for any available resources.
- Many aspirants are willing to share their study materials, including question papers and mock tests, in these communities.

4. Coaching Institutes:
- Coaching institutes that specialize in banking exams often provide their students with a set of previous year's question papers and mock tests.
- Contact reputed coaching institutes that offer IBPS RRB PO Exam preparation.
- Inquire about their study materials, including question papers and mock tests, and whether they are available for non-enrolled students as well.

Remember to solve these question papers and mock tests within the given time limit to simulate the exam environment accurately. Analyze your performance, identify areas of improvement, and revise accordingly. Good luck with your preparation!