As I understand it, that service just rounds up your spare change and then lets you do things with it. For now, use a bank account that has some sort of “spare change” functionality - Monzo comes to mind and I believe Halifax and Lloyds also offer this - and deposit it to your :freetrade: GIA or ISA. I believe that regular deposits are coming at some point, as part of the planned Auto Pilot feature.
If you mean that :Freetrade: should should have an option to reinvest profits from sales of your shares, you get that by not withdrawing the money 