Fix after testing

modules/heritiers-actor-sheet.js

@@ -158,6 +158,20 @@ export class HeritiersActorSheet extends foundry.appv1.sheets.ActorSheet {
       this.actor.incDecQuantity(li.data("item-id"), value);
     })
 
+    html.find('[data-action="quantityIncrease"]').click(event => {
+      event.preventDefault()
+      event.stopPropagation()
+      const li = $(event.currentTarget).parents(".item")
+      this.actor.incDecQuantity(li.data("item-id"), 1);
+    })
+
+    html.find('[data-action="quantityDecrease"]').click(event => {
+      event.preventDefault()
+      event.stopPropagation()
+      const li = $(event.currentTarget).parents(".item")
+      this.actor.incDecQuantity(li.data("item-id"), -1);
+    })
+
     html.find('.roll-initiative').click((event) => {
       this.actor.rollInitiative()
     })