You must attempt to motivate Grimbold to rise again and fight, for the king and for Rohan.
You urge Grimbold to rouse himself.
'Why? Why should I? Nobody will stand with me. Everyone has retreated, and the enemy cannot be kept out.'
Grimbold is at the Fords of Isen in the Westfold.
You should help Grimbold to rally his spirits and answer the call to arms once more.
Gandalf is at Erkenbrand's camp in the western Westfold.
You should speak with Gandalf.