You can use a helper entity for this kind of stuff. You create a new entity(maybe non-persistant) and set a relation to tester and a relation from the order to the helper.
Now if you have a datagrid for example, you can create a microflow button and pass on the list of selected orders.
In the microflow create the helper entity set the relation from order to helper with the new helper object. Then show a page with the helper entity where you can select a tester.
Create a new microflow from that page where you retrieve all the orders with the helper and set the relation to the selected tester.
Something along those lines should work.