You need the exact information that is on the Form 1099-B from Vanguard and the SSA-1099 from Social Security to be entered on the 2018 tax return.
You can sign onto your Vanguard account and the Form 1099-B for 2018 should be available online.
Or you may be able to import the 1099-B, see this TurboTax support FAQ - https://ttlc.intuit.com/community/entering-importing/help/how-do-i-import-my-1099/01/26254
For the SSA-1099 go to this Social Security Administration website for a replacement SSA-1099 - https://www.ssa.gov/myaccount/replacement-SSA-1099.html
