It can be challenging to find flow designer tables in your instance as most of the flow work happens on the designer. This will help you locate those tables especially the ones where the input and output variables of Flow Action Script Step.
Release or Environment
1. The configuration of the input and output variables are stored in sys_hub_step_instance table (make sure Inputs and Outputs fields are added in form layout)
2. The actual value of the input and output variables is stored in sys_hub_action_instance table (make sure Inputs and Action type.Outputs / Action type parent.Outputs / Compiled snapshot.Outputs fields are added in the form layout)
3. The rest of the Flow Designer tables can be found here: https://<instance_name>.service-now.com/sys_db_object_list.do?sysparm_query=sys_update_nameISNOTEMPTY%5EnameSTARTSWITHsys_hub