I am wondering if there is a guided tour that leaves from Dresden to Prague ( for a day trip).
You can do it on your own rather easy either by bus or train. I would recommend a night in Prague though. It is a rather beautiful city, would be a shame to just rush thru it
Yes, there are guided tours, but only in German, as far as I know.
Do it on your own - www.flixbus.de runs to Prague several times a day and back. Inexpensive.
RegioJet bus also runs throughout the day, from €9 each way.
There are also trains, bookable from www.cd.cz/eshop or www.bahn.com but be warned that in the summer these can be very crowded on this route at popular times.