I recently bought a used VPI HRX. The setup instructions show adding air to the feet. My feet don't seem to have a valve that I can see to add air.

Any help would be appreciated.
The HRX "use" to come with air bladders in the suspension towers which were prone to leaking. VPI latter replaced the air bladders with a air balls (racquetballs). The previous owner of your table probably upgraded the suspension.
IIRC, VPI did several upgrades to the original air bladder suspension.

I agree with Brf, your table probably has one of these newer suspensions.