Unfortunately there is no way to manually enter in credit card details for your clients at this time. To preserve the integrity of the credit card authorization process in Tern, clients will have to add in their own credit card details.
The credit card authorization flow is the secure way to collect payment information. Card data entered through authorization is tokenized by a PCI-certified payment provider - the card number never touches Tern's servers directly. Each authorization creates a record of the exact amount authorized, your traveler's agreement to Terms and Conditions, and their electronic signature.
Do not store full credit card numbers in contact profiles, trip notes, or other text fields. These fields are not designed for payment card data and are not protected the same way as the authorization flow.