If you can't put homebrew on the SD, hekate is probably what you want if you already boot using hekate (if not, you need an SD reader to install it too).
I tried and it didn't work, froze windows 7 explorer "doesn't answer" for few minutes, and said driver install failed. maybe it require zadig usb driver? it's not explained, and I don't like messing with drivers.
if you don't have Hekate already on your card, you can try TegraExplorer ? I don't know if it's only a file explorer on the switch, or if it can connect to PC.
HackDiskMount RCM ? this one connects to PC, but it seems it's only for eMMC partition's content. (system, user, etc.)
Don't you have Homebrew appstore on your switch ? if you properly filtered nintendo's URLs to prevent ban, you could download an FTP server to connect to your switch from Wifi.
AMS should add appstore as default bundled homebrew, it could be useful.
It doesn't seem easy to access the SD if you don't already have homebrew or RCM apps on it.
once you have access to the SD, you could try DBI from Homebrew launcher menu, which uses MTP to connect to PC.
it allows you to browse/edit the SD, backup/restore game savegames, also install games directly to SD or NAND by dropping nsp/xpi in a virtual folder, dump game cards, edit gamemods, etc.
https://github.com/rashevskyv/dbi/releases/
