"There is no way for Turbo Tax software to add the "catch up for people 50 and older contribution to the total Solo 401 K contribution."
That sounds like nonsense to me. I've never found that to be the case; I've never had any trouble entering catch-up contributions in the box provided for entering catch-up contributions. What TurboTax seems unable to do is accommodate special catch-up contributions to 403(b) and 457(b) plans, but these don't apply to a 401(k). It seems that the TurboTax representative was confused and might have been thinking about these special catch-up contributions.
I don't know why you would treat any of your elective deferral as catch-up if you have not already made the full $19,000 of regular elective deferral for 2019. That's why I assumed that you had also had made a $19,000 regular elective deferral. Or did you make an elective deferral of $12,696 so that your total regular contributions is $56,000? If you use TurboTax's Maximize function for an individual 401(k) contribution, 2019 TurboTax allocates the first $19,000 of net earnings first to the regular elective deferral, the next $37,000 to the employer contribution and the last $6,000 to the catch-up elective deferrals by implementing the worksheet in Chapter 5 of IRS Pub 560.
Are you a sole proprietor reporting on Schedule C or F or a partner in a partnership who receives a Schedule K-1 (Form 1065)? In the case where you are allocating retirement contributions reported with code R in box 13 of a Schedule K-1 (Form 1065), you just allocate between elective deferrals and employer contributions without separating elective deferrals into regular and catch-up elective deferrals.
