2016 Prius Blend door actuator noise at start up.

the should be youtube videos of gen 3. it's a big job, requiring removal of the dash and related parts.
for gen 4, you might need the service manual

 

The unit has a few different door actuators. I haven't seen a gen 4 specifically, but often there might be one or two actuators you can't get to without dash disassembly, one or two you can kind of squeak out if you look at it sideways long enough. I'd certainly start with the pictures in the Repair Manual or the New Car Features manual to get a starting idea.