This should not have been processed by the employer as a deemed distribution but should instead have been processed as an offset distribution. The Form 1099-R reporting an offset distribution should include code M in box 7 of the Form 1099-R, not code L. Before the end of the year, check with your former employer to see how they will be reporting it on the 2019 Form 1099-R that they will be issuing. If they did this incorrectly by handling it as a deemed distribution, have them make the correction.
Reporting a rollover of an offset distribution is reported just like the reporting of any rollover. In TurboTax you'll indicate that you moved the money to another retirement account and indicate the amount that you rolled over. You have until the due date of of your 2019 tax return, including extensions, to come up with the money to roll over an offset distribution made in 2019.
