Is there a section in TurboTax that allows me to do a catch-up contribution to my 401K?

Catch-up contributions must be made before the end of the plan year. It's too late to make catch-up elective deferrals for 2018.  Any elective deferrals you make from your pay in 2019 will be deferrals for 2019, not 2018. 

For additional information, see the IRS article Retirement Topics – Catch-up contributions.