Hi Lousie,
Did you create a new customizing request (or) Work bench request and assign it to admin user before performing the changes in designer?
If not please create a new Customizing request in SE01 and assign it to admin user from settings of Launchpad designer before performing the changes.
URL for assigning Customizing request:
https: //<host>.<domain>:<port>/sap/bc/ui5_ui5/sap/arsrvc_upb_admn/main.html?sap-client=<Client>?scope=CUST
URL for assigning Workbench request:
https: //<host>.<domain>:<port>/sap/bc/ui5_ui5/sap/arsrvc_upb_admn/main.html?sap-client=<Client>?scope=CONF
Regards
Virinchy