Flatex requires you to have an existing Computershare account. You can open one by buying a share through Give A Share, or a popular route has been through Interactive Brokers (IBKR). They can DRS quickly and for a $5(US) fee, (link to guide here).
Please Note; if you have GS2C shares, you can convert them to GME and transfer to IBKR at the same time using this guide.
Flatex may charge a fee of €80 for a DRS transfer. It is still a new process for them, so this may change.
Once your shares (and €80) are settled in Flatex, you need to use the Flatex Website and send a secure message to the support team indicating that you want to direct register your shares.
Ask for your shares to first be transferred within Clearstream from CBF to CBL (necessary to allow transfers to an external custodian).
Then provide the following information:
Computershare's DTC number: #7807.
GameStop's ISIN: US36467W1099.
Quantity of GME you want to send to Computershare.
Beneficiary owner (bfo): Usually yourself unless you want to gift the shares to somebody else with an existing Computershare account.
Your home address.
Your Flatex account number.
Your Computershare account number.
The support agent will take care of the rest.
Once the request is submitted the transfer will take 5-15 business days to process. If you're feeling uncertain you can check in with them by starting a support chat on Flatex's website.
If you have an existing Computershare account:
Your broker will transfer the shares in your name. As a result, a second account may be created for you. This can be for a few reasons, such as a middle initial existing on one account, but not the other. If your name matches exactly, then the transfer will process within 5-15 business days. If not, then it will take another 2-4 weeks for the account to be made and the DRS Account Statement sent out to you.
At this stage it is important to verify your tax status as a non-US citizen. While logged into your account, go to the My Profile tab, then “Tax Details”. A guide on how to fill in the W-8 BEN form is linked here).