As a member of the Polkadot Technical Fellowship you should set an on-chain identity for your account on the Polkadot relay chain. Your identity should also include a field github pointing to your github username. Unfortunately this is a custom field that isn't supported by the polkadot.js UI, therefore in order to set it you'll need to create the identity extrinsic yourself.
In the polkadot.js UI go to Developer > Extrinsics. Select your fellowship member account and pick the extrinsic identity.setIdentity. Below is an example screenshot of what it should look like including the github field.
Keep in mind that when filling in the data with Raw type only ASCII is accepted, therefore if you need to use UTF-8 characters (e.g. diacritics or emojis), you should convert the data to hex beforehand. For example, my legal name is "André Silva", which I need to submit as 0x416e6472c3a92053696c7661. You can use this tool to do the conversion, just disable the options Add Hex Base and Space Between Hex Values, after the conversion you should prepend the result with a single 0x and submit as Raw.
After submitting the extrinsic you won't be able to see the github field in the polkadot.js UI (custom fields aren't shown). You can confirm that everything was set correctly by checking the state (Developer > Chain State > identity.identityOf), or by using a block explorer like Statescan which shows custom fields.
After your identity is properly set you can get a judgment on it from one of the existing registrars. For instructions on how to get a judgment from the W3F registrar check this page which contains links to instructions. Due to the custom field in your identity the automated verification process won't work and you'll need to join the support channel on matrix to complete the verification.