Yellow color-coding indicates wiring and connectors associated with supplemental restraint systems (SRS), such as airbags, seat belt pretensioners, or their associated sensors. Toyota’s Repair Manual for the 2013 Prius explains how to release the locking mechanism for the pretensioner connector in the photo. I don’t mean to be unhelpful, but I’m not sure I should share only that information here, since anyone working on SRS parts needs to refer to the same manual for other important safety instructions. One essential precaution is to disconnect the negative (–) terminal of the auxiliary battery and then wait at least 90 seconds before starting work, but there are others, too numerous to reproduce here. For the original poster is in Portland, Oregon, note that the Portland Public Library—like many others—sponsors free access for its patrons to the ChiltonLibrary database, which includes most of the text and illustrations from the Repair Manual. After selecting 2013 Toyota Prius, look under Repair > Body > Interior > Seat Belt > Front Seat Outer Belt Assembly and Repair > Chassis Electrical > Supplemental Restraint Systems > Airbag System > Precaution. The manual is also available by subscription to techinfo.toyota.com.
If the airbag has not deployed, you can pry slowly the yellow part out a little, then you should be able to unplug it. If the airbag has deployed, you can't unplug it
