MS-900 has been replaced with AB-900
MS-900
http://www.cbrandon.com/vids/MS-900%20Microsoft%20365%20Fundamentals%20Study%20Cram.mp4
AB-900
http://www.cbrandon.com/vids/AB-900%20Study%20Cram%20-%20Microsoft%20365%20Certified%20Copilot%20and%20Agent%20Administration%20Fundamentals.mp4
Study Guide and Test: https://learn.microsoft.com/en-us/training/browse/?resource_type=course