Charitable donations will not show up on your 1099-B tax statement. Since you gave away shares with gains instead of selling them, this action will not be reported to the IRS and is not a taxable event.
If you itemize your deductions to take charitable deductions, you (or your tax software or accountant) will report the donation when you file your taxes. Your donation receipts, available in your Betterment account in Documents section of the Activity tab, will be useful in this process. Donation receipts are kept for your records and are not filed with your taxes.
For non-cash charitable contributions (including share donations from Betterment) over $500, you must fill in a Form-8283 when you file your taxes.
If you’re using TurboTax or another tax filing software, it will typically ask you about your donations details and fill out the Form-8283 for you.
This information is not meant to be tax advice.