You should revise the first 5 topics: Atomic Structure, Bonding, Quantitative Chemistry, Chemical Changes and Energy Changes.
Below are links to the specifications, BBC Bitesize revion website and, for each topic, a checklist & some questions (some of these “quickfire question sheets have a linked YouTube video).
GCSE Specification (first 5 topics)
1. Atomic structure & Periodic Table checklist
1. Atomic Structure & Periodic Table QuickFire Questions
2. Bonding, Structure & Properties QuickFire Questions
3. Quantitative QuickFire Questions