Well, the first thing to do is to try and avoid a dispute by having a constructive discussion about the areas in which you disagree so you can ideally avoid a dispute all together or, failing that, reduce the areas of contention which will mean it is less burdensome on all parties.
Secondly, I notice you say the "PM has ... extended the period to allow him to assess." If I read it correctly, the PM has extended it without your agreement, which the contract does not give him or her authority to do ... in fact it does not give the PM and the Contractor in agreement authority to do this. So you could enact the provisions of clause 64.4 (assuming this is NEC3) to get 'deemed' acceptance of your original quotation.
So - now to answer your question ! - assuming you are under NEC3 and W2 has been used, then you need to give "a notice of the adjudication to the other Party with a brief description ofd the dispute and the decision which he wishes the Adjudicator to make."
However, from your description, a dispute is not yet fully formed.