To change the permission mode of Project Online, Please follow the below steps.
Logged in with an Office 365 tenant admin account: Click Admin
Click SharePoint, that will take you to the SharePoint Admin Center:
From this page, select the PWA site collection (Link: https://PWATech.sharepoint.com/sites/pwa/) then click the Settings link under the Project Web App menu as displayed below
This will load the Settings page for the Project Web App site:
Select Project Permission Mode and press OK.