The student should be instructed to go to the Chair's Suite and request to borrow a laptop.
If you have elected to sign-out a laptop for your assessment, you should not provide that device to a student who has forgotten their laptop. That device is for students who may have encountered a malfunction on their device, which they remembered to bring with them to the assessment.
If no laptops are available, then provide the student with a hard copy exam.
Special note for Testing Center administrations:
The Testing Center has a computer available as a back-up. A student who is completing their assessment at the Testing Center, but who has forgotten their laptop, may use the Testing Center computer instead. That is, the student does not need to retrieve a laptop from the Chair's Suite.