Ruth, your Trust will have a training department or similar, who will presumably have arranged for this course/funding for it. Contact them and explain your position in confidence, and ask if the location can be changed.
However - you say "this week" so if you mean tomorrow or Friday, that is probably too short notice now..... how long have you known about this? speak to the training department, speak to the L&D manager in your boss's absence and explain what's happened and how awkward it would be for you to be in that location. If you'd asked me, I would understand and do what i could to facilitate a change.
Finger crossed - let us know how you get on.