Sawasdee khrap, khun Nan.

Warning-as we have seen several from other Pass-users from this beautiful country Muang Thai: you need to set the calender on the phone to the western style, with the buddhist time will not work and give problems.

Choke dee duay.

Yes you can. There are 3 steps and the pass is only activated after the third step:

https://www.eurail.com/en/eurail-passes/eurail-mobile-pass/getting-started

You can even activate the pass to test if it works and then deactivate again.

Since you're from Thailand, do check the requirements, especially the calendar settings:

https://eurail.zendesk.com/hc/en-001/articles/5545614121757-Basics-to-run-the-app