The amount listed on my 1098-T for tuition expenses is listed in GBP, not USD. What do I do?

You will have to enter the amounts using the foreign currency conversions. See the website below for the conversions accepted by the IRS Foreign Currency and Currency Exchange Rates

Convert before you enter in TurboTax.  What you enter does not have to match the exact 1098-T. 

The 1098-T is only an informational document. The numbers on it are not required to be entered onto your tax return. However receipt of a 1098-T frequently means you are either eligible for a tuition credit or possibly your student has taxable scholarship income. 

You claim the tuition credit, or report scholarship income, based on your own financial records, not the 1098-T. 

If you claim the tuition credit, you do need to report that you got one or that you qualify for an exception (the TurboTax interview will handle this)