Congrats! You have done well to win yourself RM50 credit free roaming!
All you need to do is sign up here , for a free account.
And once FlexiRoam has your sign-in email & mobile, FlexiRoam will put the credit into your account for you, so all you have to do is to check that your account has received the credit after.
You won’t have to do anything except sign-up. FlexiRoam has clear instructions on their website on how to activate your free credit when you roam.