How to contact HR as former employee

My last day was April 29th and I have not received my full paycheck from working that day. My manager forgot to put in my mileage for me doing inventory at a store in another state, and says he cannot do anything because I no longer work there. I sent him my paystub and the mileage again, and he said he'd have to contact HR because I had since quit. It's been over a month now and I don't want to keep going back and forth with him. I'd rather just contact HR myself at this point but I'm not sure how or what would be the best way to get ahold of them for this situation. I no longer have access to workday since my login has been deactivated, so I'm not sure where to look for resources or how to contact HR partner/team member services. Is there a general email or phone number to get ahold of them and will they still be able to talk to me as a former employee?