I think you should try to 're-introduce' them. Get a someone to hold your dog either on a lead, his collar or just firmly holding him and you can hold your cat. Let them check eachother out but don't force them together and don't hold them too close to eachother. Give them a few minutes to sniff eachother and give them each a treat while they are there that way they will asociate eachother with a treat so it will be a nice experiance for them to be together. Do this a few times a day and see if it helps but don't hold them together for too long or they might get aggravated. Hope I can help!