Registering an username (contested / not contested) is currently not supported in Dash Evo Tool. It will be supported through a future update.
Hopefully through a future update that will be released soon.
Through TUI (terminal user interface) : more like a developer tool, only tech savy persons use it. Can create contested usernames and not-contested usernames.
Through DashMoney.io : can register only not-contested usernames
Through DashPay mobile wallet Dapp (Android) : currently not released yet in Play Store, but available as beta to use on Mainnet. Can register contested and not-contested usernames
Through Platform CLI : can register contested and not-contested usernames
Soon through Dash Evo Tool : can register contested and not contested usernames
Personally i am waiting for the DashPay mobile wallet Dapp (Android) to get released to the Play Store.
Note : registering an username does seem to require having an identity, which is something you can not create just yet with Platform CLI.
But it can register an username for you, if you already have an identity.
Maybe use DashMoney.io (https://dashmoney.io/) to create an Identity and then use Platform CLI to register a contested username ?
(DashMoney.io does not allow registering contested usernames). DashMoney and pshenmic are both active on Discord (general channel), so maybe ask them if that could work.
Update : i asked on Discord
This question remains : does DashMoney.io give you the privatekey of your registered identity?