Apex Class:

global class approvalRecall {
    webservice static void recallApproval(Id recId) {       
        List<ProcessInstanceWorkitem> piwi = [SELECT Id, ProcessInstanceId, ProcessInstance.TargetObjectId FROM ProcessInstanceWorkitem WHERE ProcessInstance.TargetObjectId =: recId];
        Approval.ProcessWorkitemRequest req = new Approval.ProcessWorkitemRequest();
        req.setAction('Removed');       
        req.setWorkitemId(piwi.get(0).Id);
  
        Approval.process(req,false);
    }
}

Custom Button Javascript:

{!REQUIRESCRIPT("/soap/ajax/15.0/connection.js")}
{!REQUIRESCRIPT("/soap/ajax/15.0/apex.js")}

var r = confirm("Are you sure want to recall the approval process?");

if(r == true) {

sforce.apex.execute("approvalRecall","recallApproval",{ID:"{!Member__c.Id}"});

alert("Approval has been recalled");

window.open('/{!Member__c.Id}');

}

else {

alert("Recall Cancelled");

}

 Output: