If I need to update my citizenship status in Turbotax to lawful permanent resident (green card holder), how do I get to the Personal Info Summary screen?

TurboTax doesn't ask your citizenship status. There is no place to enter it.

If you were a resident alien based on the substantial presence test, and you have now gotten a green card, it doesn't make any difference for tax purposes. You are still a resident alien. A resident alien is treated the same as a U.S. citizen for tax purposes, so TurboTax doesn't need to know whether you are a citizen or a resident alien.

If you were a nonresident alien, you should not have been using TurboTax. You should have filed Form 1040-NR, which TurboTax does not support.

If your status changed from nonresident alien to resident alien during the year, see the section on dual-status aliens in IRS Publication 519, U.S. Tax Guide for Aliens.