Assuming your client contributed to the Roth IRA and the contribution along with accrued earnings/losses are to be recharacterized to a traditional IRA before the due date, you don't need to report the distribution on Line 4a (given the recharacterization happens in 2019) on either the 2018 or 2019 return but should attach a statement to explain the recharacterization and amounts involved.  You can see the instructions on F.8606 for more details: https://www.irs.gov/instructions/i8606#idm140149371801472