How can my sister correct her entry stamp from tourist to non-immigrant ED in Thailand?

Greetings. My sister is a new fellow in Siriraj who just arrived last week (1st arrival in thailand, in Don Mueang airport). By fellow, her medical training here will last for a year.

She was about to open a bank account and upon reviewing her documents, she was told by the bank that her stamp upon entry was wrong, because it was stamped as a tourist entry, not as a non-immig ED entry, so her stamp states a date that is shorter than her visa, and should have it corrected. The international affairs office just told her to go back to the immigration office and have it corrected but didn't give her any more specific instructions. We tried going back but they wouldn't understand us, and said we cannot enter the immigration office.

Her educ visa is an e-visa because that is what they provided her upon application.

We were given a number to call but no one understands us. Would anyone happen to have an idea how we could have this resolved? We were told we have to correct it asap. Thank you very much.