Welcome to the forum 
I can see @Long-John-Silver has given you the link to the testing guide
That should tell you all you need to know, but in summary:
- Submit reviews for products you already own (as long as it’s stocked by LH, you don’t have to have bought it from here)
- Have patience, there are a lot more volunteers than testers available
- Understand that being selected to test is a privilege and not guaranteed
The Sex Toy Tester - Chit-Chat might also have answers to any questions you have 