Hi Klonan,
Thank you for your reply.
All right, I will try to do so.

Oops, I apologise. Thank you for the instructions link.

I updated the title and here are the Save file and the log.

Step 1: created a 15 stops and 5 trains network. One of the station is called "Starter1_Refuel[*]Coal" (with the coal icon at the end of the name) .

Step 2: All trains are assigned the same interrupt to refuel called "Refuel" with Condition "Fuel(any)<40" and Target: "Starter1_Refuel[*]Coal ...