Configure the subroutine to take a single DINT as an input, and to return a single DINT as a return value.
In the subroutine, use a local DINT tag as the by-value pass of the input DINT, increment it, and return the local DINT back to the subroutine call.
Note that the JSR must be configured with one input parameter, and the same parameter as a return value.
In 16+, use an AOI, with In/Out parameter.