When you open the app, select "Launch Band Selection." That will open a menu that likely looks familar. Now, swipe from the left, or tap the menu bar at the top. Select "Band Selection" again. This will show you all of LTE and NR bands your phone is capable of receiving. Select the band(s) you want, then toggle "Selection" on the top right. Apologies if you already tried that, but it sounded like you only got to the first menu.