URGENT: Order Printer Variable

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Dear Community, I am using Order Printer App for invoices and for refunds.
I want my refund template to also have a number which should be GS-order_number-1000. This is for taxing purposes. I have this code so far:
<li class="order_details">
<span class="order-details-title editable" data-key="number"> Refund-Nr. </span>
{% for transaction in refund_transactions %}
{% endfor %}
What I need is for the "-1000" to also be variable. I need the first refund to be GS-order_number-1000, the second GS-order_number-1001, the third GS-order_number-1002, and so on. I am not sure how I can manage to make the "-1000" dynamic. Any ideas? I got in touch with the Shopify Theme and they told me that there is no easy solution for this. They suggested using a different app or getting in contact with an expert. Before I do this I would really like to receive your help if possible. Thank you so much in advance!