Audible does not let you directly gift individual credits to another account
To give someone Audible access, buy them an Audible gift membership instead
Go to the Audible gift membership page
Choose the membership length you want to gift
Enter the recipient’s name and email address
Complete the purchase
The recipient will receive instructions to redeem the gift membership
If you want to help them get a specific audiobook, you can also buy the audiobook as a gift instead of gifting credits