Hi @lewtun. Thanks very much for that - it works now. I will check out the docs for some further information.
Also, I am trying to add special tokens to my model using the code found here: Tokenizer — transformers 2.11.0 documentation
Here is the code I am using:
# Let's see how to increase the vocabulary of Bert model and tokenizer
tokenizer = BertTokenizer.from_pretrained('bert-base-uncased')
model = BertModel.from_pretrained('bert-base-uncased')

num_added_toks = tokenizer.add_tokens(['🥵', '👏'])
print('We have added', num_added_toks, 'tokens')
model.resize_token_embeddings(len(tokenizer))  # Notice: resize_token_embeddings expect to receive the full size of the new vocabulary, i.e. the length of the tokenizer

The error:
NameError                                 Traceback (most recent call last)

<ipython-input-27-203dc3e7172a> in <module>()
      1 # Let's see how to increase the vocabulary of Bert model and tokenizer
----> 2 tokenizer = BertTokenizer.from_pretrained('bert-base-uncased')
      3 model = BertModel.from_pretrained('bert-base-uncased')
      4 
      5 num_added_toks = tokenizer.add_tokens(['🥵', '👏'])

NameError: name 'BertTokenizer' is not defined