Hi My!



 Myailab:

is there any way I can just train my model on new class and get the predictions for all four classes?


If you literally mean train your model with batches that consist
solely of samples of the new class, then, no, this won’t work.  As
it trains, your model will simply learn to predict your new class
all of the time, regardless of the input, and, with respect to your
single-class training set, it will always be right.
If you are asking something  else, please clarify.
Best.
K. Frank