If your microSD card isn't recognised and (as your link suggests) you're in the USA, follow the steps here or, if you find that no other microSD cards are recognised either, click on the link at the foot of the page for the 'online repair process'. As you go through that, you'll be provided with the address to send your Nintendo Switch to:
https://en-americas-support.nintendo.com/app/answers/detail/a_id/22482/~/microsd-card-is-not-recognized
You should note however that Covid-19 has led to delays in Nintendo's repair services. (Click 'Set up a repair' in your own link for information about the current situation).
If you're in the UK (where The Answerbank is based), this page duplicates the information from my US link above but provides a link (labelled 'click here', at the foot of the page) to the UK repair system. (Once again, you'll be provided with an address as part of the registration system):
https://www.nintendo.co.uk/Support/Nintendo-Switch/microSD-Card-is-Not-Recognised-1497989.html
An additional hint from me: If your SD card isn't recognised in your Switch, try connecting it (via an adapter) to a PC. If it's recognised there it might then become recognisable in your Switch again. (I've absolutely no idea why that can happen but experience has taught me that if an external drive isn't recognised in one device, simply getting it recognised in a different one can be all that's needed to render it visible again in the first device. There seems to be no logical reason for that but it's helped me out of a hole on many occasions!).
If your Switch won't recognise one card (and the above hint doesn't make it visible to your Switch again) but it will recognise others then, if your PC can 'see' the dodgy card, you can transfer the data from that card across to your PC and subsequently across to a new blank card.