Under Procurement > Authorization > Purchase Authorization Basic Data, add the user in the Authorizer ID for the relevant company. Optionally add authorization amount, Validity should be Active on the line. You may define authorization groups and routing templates as well per your requirement

Under the page Purchase Order Authorization, you can see list of POs along with authorizer IDs

Additionally @Nagah.khaled please see this link, it explains well the entire setup needed

https://docs.ifs.com/ifsclouddocs/default.htm?openpage=https://docs.ifs.com/ifsclouddocs/Procurement/AboutPurchaseAuthorization.htm