Change of client,location.How to process h1b transfer?

My petition was filed for client A in another location. Now I am getting offer within same employer but different client B to work in their location.I am asked to file a new ammendment for me to work with client B. Can I travel after filing the ammendment or should i wait till entire premium process is over?
Is there an option where I can travel to the stamped location and follow any process?

Note:Never travelled to US.