There is little you are going to be able to do today. If his gums or tongue are pale or white he should be seen by an emergency vet today. Otherwise if this is related to severe gingivitis and tooth infection he will need to see his vet tomorrow for antibiotics and to get him set up for a dental cleaning. He may have a few teeth that need to be removed but getting the tartar off of his teeth and out from under the gums will result in him feeling much better faster than just with antibiotics alone. Many pet owners do not realize the implications of poor dental health. Not only does this affect his teeth and gums but bacteria is able to gain access to his blood stream and can affect his heart, liver, kidney's and bladder as well. So, once his teeth are cleaned I would start keeping up on his teeth with every day or every other day brushing. Schnauzers are one of the more common breeds to develop severe teeth and gum issues. It comes with the breed. I wish there were more you could do but at this time and without a vet you will have to wait this out until you see your regular veterinarian. Again if his gums are pale or tongue is pale or white in color then he may have something more than just oral health issues that should not be taXXXXX XXXXXkely. He may have developed a clotting issue or has an immune mediated anemia that would need to be addressed as soon as possible.
I was worried about the Immune mediated anemia (IMHA). Once they get it all figured out and determine whether this is regenerative or not his treatment may not be too expensive. Hopefully, they have started him on steroids. Response should be seen within a couple of days if they have. He may or may not need to be on these long term but they also are not too expensive either. Testing after stable will decrease to every few weeks.
Good Luck, sorry about the diagnosis he has received.