Steps in updating single field for multiple (selected) lists items

i’m very new in SharePoint and wanted to seek some help. I have created a simple SP list that has a simple approval process…all is working fine…however, I was task to enhance it by allowing the approval of multiple/selected list items which I have no idea how to proceed.

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Basically, it’s just to select the lists items and have a custom action/button that when click, it will just update and set the value of the field “Status” from “Submitted for Approval” to “APPROVED”.

We are using SP2010 and SPD2010

Thank you.