Sorry to state the obvious, but an architect should always know what to do when your initial planning application has been refused.
I can give you a brief outline to help you.
Firstly look at the reasons for the refusal, it could be something very simple which may only require the drawings to be amended slightly.
For larger objections and here's a few that I mean 'large'
Extension ratio to large to existing structure
Extension not in keeping with the surrounding residences
And let's not forget that old chestnut, the neighbours have lodged objections.
If it is any of the larger ones, don't get disheartened. A good architect will address the objections and re-draw accordingly.
Then submit the revised drawings for COMMENT, to your friendly local planning department. I suppose I look upon this as a dummy run, they may say Ice there's no problem now so submit. Or they may say Ice your client cannot have a 16m high extension in the form of an igloo in their back garden, and you should know better.
If your architect does not have a good relationship with the planning department or more importantly does not have local knowledge of the area ( to know the quirks that all councils have in their planning criteria), then terminate the contract.
You really need a local architect who understands the area and what is permissible in the locality.
One other thing DO NOT engage one of these charlatan 'planning' companies who in the world of architecture are nothing better than ambulance chasers. They pray on the unsuspecting poor souls that are hoodwinked into believing these companies have special powers and will make everything alright if you cross their palms with 30 pieces of gold.
They do nothing of the sort, every week they scour the planning applications denied listings and target their victims.
Good luck OP, I hope I have managed to help you.