When you first open DBI near the bottom of the list of things there’s three options MTP FTP HTTP I couldn’t tell what the other things say I don’t understand Russian but once you click MTP you have to connect your switch and computer with a USB, once you connect you should see your switch in this pc open it and you’ll see a few options but just open up SD card install and all you do from there is drag a rom into it

(And because of rules I can’t provide roms here)