Citibank HK 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, guide here.
Therefore, they will ask you for a Computershare account number. For security reasons it is not recommended to give this information to your broker, but in this case there may not be another choice. With Computershare accounts, the account number is the "key" that allows brokers to authorize a transfer of shares out of the DRS and back to the broker.
If you provide your account number to initiate the transfer, it is recommended to protect your Computershare account by making a small change to your name or address to block any unauthorized attempts at withdrawing your direct registered shares. Such as adding or removing a middle initial, or making a subtle enough change to your address that you can still receive your snail mail (add or remove a borough, or a space in your postal/zip code).
Only do this when you are confident you are finished transferring your shares from your broker to the DRS, and if you are confident you do not want to move your shares back to your broker.
How to transfer:
Citibank HK charges a $50(US) fee for each DRS transfer. This means each time you want to direct register shares of a specific stock you are charged $50(US).
Once your shares and $50 are settled in Citibank HK, you can send them a Letter of Direction. This can be handwritten or typed, but it must be signed with wet ink. You can write it informally, or use the following templates: GameStop specific template, blank template for any stock.
Writing it yourself?
Be sure to include:
Say: “I want an outbound DRS transfer of my GME shares to Computershare”.
Put a statement agreeing to the fees- eg. I agree to the fee of $50 (US).
Your account number, full name, phone number, email address, Tax ID.
The stock (GameStop), its ticker (GME), and its CUSIP (36467W109).
How many shares you want to transfer.
The Transfer Agent's name, DTC number, and address. In GameStop's case that's: Computershare US. DTC# 7807. Computershare Trust Company, N.A., P.O. Box 505005, Louisville, KY 40233-5005.
Your Computershare account number.
If you want the shares ordered in Last In First Out (newest shares transferred first), or First In First Out (oldest shares transferred first).
With the Letter of Direction completed and signed, scan it in.
Scan your latest Computershare Statement proving your account number.
You have to go to a physical branch to submit the transfer request. Bring copies of the documents with you.
Once you have given Citibank HK the Letter of Direction, the transfer will take 10-15 business days to process. If you're feeling uncertain you can check in with them by starting a support chat on Citibank HK's website.
If you have an existing Computershare account:
Your broker will DRS transfer the shares based on your name and address. 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 and address match exactly, then the transfer will process within the normal amount of time. 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.
Tax Form:
At this stage it is important to first 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.
You must fill in the W-8 BEN form before you buy any shares through Computershare, or add your banking information (especially if it's a US dollar account). Otherwise you will be assumed to be a US citizen.