Wrong mail address in Access Request Settings

RequestAccessEmail property is supported in SharePoint Online. You can use the below PowerShell script to set the RequestAccessEmail. 

$SiteUrl = "https://<TenantName>.sharepoint.com/sites/<Sitename>" 
$UserName = "admin@<TenantName>..onmicrosoft.com" 
$Password ="password"
$loadInfo1 = [System.Reflection.Assembly]::LoadWithPartialName("Microsoft.SharePoint.Client")
$loadInfo2 = [System.Reflection.Assembly]::LoadWithPartialName("Microsoft.SharePoint.Client.Runtime")
$loadInfo3 = [System.Reflection.Assembly]::LoadWithPartialName("Microsoft.SharePoint.Client.UserProfiles")
#$sstr = ConvertTo-SecureString -string $AdminPass -AsPlainText -Force
$Securepass = ConvertTo-SecureString $Password -AsPlainText -Force
$context = New-Object Microsoft.SharePoint.Client.ClientContext($SiteUrl)
$context.Credentials = New-Object Microsoft.SharePoint.Client.SharePointOnlineCredentials($UserName,$Securepass)
$Web = $context.Web
$AllProperties=$Web.AllProperties
$context.Load($Web)
$context.Load($AllProperties)
$context.ExecuteQuery()
$Web.RequestAccessEmail="alexd@<TenantName>.onmicrosoft.com"
$web.Update();
$web.Context.ExecuteQuery()