You should immediately disconnect the PIN pad from the computer but avoid disconnecting it from power.  You should also disconnect the POS workstation from the network but leave it turned-on.  Put a note on the POS terminal 

Then you should carefully inspect all other PIN pads and POS devices for tampering.  If nothing is found, you can reasonably continue transacting business on the other POS stations.  Credit card skimmers work by stealing card data at the point of interaction – when the customer swipes or taps their card.

Next, determine when the skimmer was installed.  Review device inspection logs, opening/closing manager notes, and/or hand-off lists.  Review security camera footage.  

A card skimmer is potentially a serious data breach.  Once you have an idea of the size of the problem – the length of time the skimmer was in use – you should notify your manager, owner, and Epicor (or other POS system provider). 

And, you should definitely activate your company’s Incident Response Plan.