I connected a flow sensor to SMARTDAC+ GX/GP series, but can you tell me how to configure flow measurement?

You can use the Scaling function to measure flow. The following is an example using main unit slot 1, channel 1 (0101), with an input signal of 1–5 VDC at 0.0–100.0 m³/h.
Go to MENU key > Browse tab > Setting >Setting menu > AI channel settings > Range. Under Computation, tap Linear scaling, and then set the physical quantities. For details, see “Advanced Operation (Various settings and operation)” in the first step guide (IM 04L51B01-02EN).