Welcome to the forum.
Other than Importing those files (what format/CODEC are they?), into a single Timeline, then adjusting the Volume of the first, Rt-clicking on that and choosing Copy, then Selecting all of the rest, Rt-clicking on them, and then choosing Paste Attributes. You could then use the WAB (Work Area Bar) to Share each Clip as a new file, or could Share the entire Timeline for one long file. Otherwise, there is no way to batch process.
If I have to do that, it is just as easy to watch them in Premiere Elements one by one and adjust the volume as I watch them.
Thanks for your help.
The problem with "batch processing," along the lines of doing so with Still Images in PS with Actions, is how non-destructive NLE (Non Linear Editor) programs, like PrE work. They do not actually have the Source Files in the Project, but just links to those Source Files. What we see on the Timeline is just a proxy/representation of what will be done, when that Timeline is Exported/Shared. The Project file contains NO media, but links to it with instructions on what data will be extracted and used, from the actual media files, plus instructions on how to then process those data, such as Effects added/adjusted. Those original media files are never touched, only read from. Nothing exists, beyond some XML database and instruction code - UNTIL one does the Export/Share. When one does a Save (any type) in an NLE, only that XML database and instruction code is written - no media yet. When one does a Save in PS, it IS the Image, the media file, that is Saved.