Customising the reassign menu on Approvals

Hi all,

I'm quite new to the Power Automate technology and am still trying to find my way around. 

The question I have concerns the Approvals side of things. I have created an approval flow and have enabled the 'enable reassignment' option to allow an approver to reassign the task to a colleague. However, I can't find any obvious way of customising the list of available users.

What I'm hoping to do is only allow reassignment to a member of staff who is in a particular SharePoint list or, if this is not possible, filter the default list. Basically, so the approver can only reassign the task to a member of their own department.

Is this possible?

Thanks for any advice you can offer.

Mark