Warble on my Reel to Reel (Emergency!!!)

[Alaking]

Hey guys & gals. got a question, hoping there is a quick fix.
my band is currently trying to record on to a ReVox Reel to Reel tape deck. We also rented a bunch of fancy equipment we rented for a week, and are trying to get some songs done ASAP.

There is a slight warble on the tape deck during playback. Does anyone know if this is something complicated to fix?? We have the back up option of just recording on the 'ol computer, but we would perfer to get this thing rolling.

Thanks a ton for any suggestions!

cheers!
JS