Below is the url rewrite rule added in azure webapp config to redirect the site to any new location, let it be a SPO site or any other web url. The sample below redirects to the microsoft password reset page.
<?xml version="1.0" encoding="UTF-8"?>
<configuration>
<system.webServer>
<rewrite>
<rules>
<rule name="SimpleURL" patternSyntax="ECMAScript" stopProcessing="true">
<match url="(.*)"/>
<action type="Redirect" url="https://aka.ms/sspr/?whr=domain" redirectType="Permanent" appendQueryString="true" />
</rule>
</rules>
</rewrite>
</system.webServer>
</configuration>