Considering there was a talk on LD's Chat section about how CPR should be taught in schools but it isn't, this is sort of the next best thing without spending any money (but may apply in some cases).
However, while it is free you'll need to study it carefully to pass the course which doesn't just help you on pass it but also in the event you need to use the skill in real life.
To make things easier, it includes sample videos to help you through it,
- CPR & First Aid
- CPR Certification Online
- Online CPR & First Aid Certification
- ProCPR - Pro Training Courses