You can not convert 2019 data back to 2018 data. You may have to contact support for help. https://proconnect.intuit.com/community/help-articles/help/how-to-contact-lacerte-for-help/00/4691

You should have followed these steps: 

(A) Convert UT 2018 to Lacerte 2018

(B) Spend time to review the Lacerte data for  2018 to (a) get familiar with the program and (b) review state return(s) and (c) check depreciation.

(C) After a quick review, go to Screen 3 and look for a check mark, right above the header for Organizer Miscellaneous - remove that check mark 

(D) Proforma from the 2018 program to 2019

(E) Edit settings and produce the Organizer from the 2018 program.