How do I report Roth Solo 401K contributions in 2018 TURBOTAX

I was previously a W-2 employee where I built a Roth 401K balance. Upon leaving that company, I rolled said Roth 401K over to my personal advisor's control where the funds are invested in a TD Ameritrade Roth 401K account. This year I am again consulting, but now as a 1099 employee. This same 401K account can be used for my solo contributions. How do I report my contributions into this Roth 401K account (as the 'solo' employer - i.e. me)?  Is the reporting done outside my tax filing?  If so, does anyone know how this is reported (there are limits based on my income).