Ordinarily arbitration is used because the parties agreed in their agreement to use arbitration.
However, it is still possible, notwithstanding the commencement of the dispute, to agree with the party with whom you are in dispute that arbitration is an appropriate dispute resolving mechanism for the dispute.
The first step is to identify a suitable arbitrator with expertise in the subject matter of the dispute or a suitable organisation to appoint an arbitrator and ask for their assistance.
A good arbitrator will quickly get the parties to agree to an arbitration process and the dispute process will commence.