Regarding add extra class in fine-tune model

Hello Everyone
I have trained Bert model for classification task for 31 classes.
Now, I want to add one or two extra classes in fine-tune model.
Idea is that, I don’t want to fine-tune entire model, but I can load previous fine-tune model and add only extra data(class)

I tried but it is showing an error as mismatch size, offcourse, that will happend because earlier I have fine-tune the model for 31 classes

So how I can add extra class? something I have to remove last layer or else

Can anyone help in this context?