You say "hello” or "good day” and show your pass.

If you have a mobile pass, check this page:

https://www.interrail.eu/en/interrail-passes/interrail-mobile-pass/getting-started

If you have a paper pass, check this page:

https://www.interrail.eu/en/interrail-passes/what-is-interrail/how-use-your-interrail-pass

Nothing-you show your pass with valid and with trip being made QR-code.

BUT; you can say hello, or ciao- or dober dan-depending on where you are. Or tell : INterRail.

Again: well over 90% of all trains that run in EUR and accept passes are without any RES needed or even the chance to do it.

Thanks. I will implement your answer.