NEED HELP emails not showing when switched to old outlook app

Hi! I need to back up my school email account since I'm graduating, and school IT suggested to export into .pst file then import into a new alumni account. I searched up tutorials and realize this can only be accomplished through the old version of outlook app, but when I switch back none of the emails show, and I tried to follow through the back up process but the .pst file turn out to be 375kb. I'm using windows and the new outlook that I've been using works perfectly. Please help.....