After upgrading to SAP GUI 7.70 you can change the default browser from Internet Explorer to Edge.
Prerequisite: install WebView2
First read OSS note 2913405 – SAP GUI for Windows: Dependencies to browsers / browser controls. This note describes the need for you to download and install the Microsoft WebView2 framework:
Switch browser setting
Now you can go to the settings of you SAP 7.70 GUI and change the default browser in the Interaction Design/ Control Settings:
If fallback to Internet Explorer is still required, read this note: 2957665 – SAP GUI HTML Control: Browser Control Fallback Configuration.