You enter it under the Deductions & Credits tab in the Charitable Contributions section. But be aware it may not help tax-wise. Charitable donations are a SCH A deduction. Until the total of all your itemized deductions exceed your standard deduction (which has doubled for the 2018 tax year) they will make absolutely no difference what-so-ever to your tax liability.
so if you're filing single or MFS, your standard deduction is $12,000. For MFJ it's $24,000. so it would take a "LOT" of itemized deductions before you'll see any impact on your tax liability.
