Referencing your post "I've done a single interview > 15 years ago, unpublished."
I do not understand how that prohibits or prevents you from requesting that the interviewee turn up their microphone.
That said:
On your computer right click the small speaker icon usually located in the lower right screen corner.
Doing so should open up a pop up Window with various audio related choices.
First run the audio troubleshooter - the trouble shooter may find and fix something.
Then check both "Open volume mixer" and "Sound settings".
Each option will lead you to any number of other windows, tabs, configuration settings, and perferences.
Explore all of the possible choices being careful not to change anything. Make some notes then go back and make a changes (only one change at a time) that may help control the volume and keep it constant so you can turn up your volume and not have a loud interviewee hurt your ears.
= = = =
If nothing seems applicable or workable there then check loudness via the following link:
https://allthings.how/how-to-enable...n,system settings that open in the right pane.
You do not need to download or install anything as the link tries to get you to do.
Instead just follow through on the steps and corresponding configuration settings to enable
"loudness equalization".
Speakers Properties - Loudness Equalization.,
Try that to determine if the speaker volume remains constant despite a loud interviewee.