Hello Kaustubh,
just convert string to number using "Scan from String" and then round your number (multiply by 1000, round to nearest, divide by 1000).
Perhaps the formatting of the output indicator may help: just show the number with only 3 decimals after the point.
Best regards,
GerdW
using LV2016/2019/2021 on Win10/11+cRIO, TestStand2016/2019