Hi, I have a subprocess that must be executed in multiple istances (one at time)

You can create a multiple value PV in your main process and map this multiple valued PV to a similar multiple value PV in the sub process. Make sure that you pass the multiple valued PV in the main process to the sub process byreference.
Keep appending the values of each instance of the subprocess to this multiple valued PV in the sub process.

The only things I know is to set the inputs and the outputs in the Setup tab of the SubProc task. Where I set variables are passed byreference and not by value?
Thanks

On how to use byreference(),you can refer the link forum.appian.com/.../Process_Variables_by_Reference

Thank you..And last question..Every instance of the subprocess has always the same tp!instanceindex = 1..I thought this varible var incremental

By any chance are you referring to the instance index of the sub process (the iteration count of the sub process)? If you need this in your sub process,then you have to pass the index from the parent process to the sub process.

Yes I need to use the iteration count of the subprocess..I've tried your suggestion but there aren't the task properties in the editor for Input Variables..I'm looking for tp!instanceindex

You could have a single value (Number type) PV in the main process. In the sub process have a similar single value PV. Pass the single valued PV from the main process to the sub process. Make sure that you pass this PV to the sub process byreference.
In the sub process, keep incrementing the value of this PV by 1 (in a script task) each time an instance of the sub process runs.