Hi @Laura_Amber,
Do you want to type a group email address within Assigned to field of "Start an approval" action?
The group email address is not supported in Assigned to field of "Start an approval" action within Microsoft Flow currently, the Assigned to field only support specific personal email address.
If you want to send the approval email to multiple approvers, you could consider type multiple approvers' email address within Assigned to field and separated by a semicolon (;) .

In addition, if you would like this feature to be added in Microsoft Flow, please submit an idea to Flow Ideas Forum:
https://powerusers.microsoft.com/t5/Flow-Ideas/idb-p/FlowIdeas
Best regards,
Kris