If you choose “Settings” when you enter to your bio link page. You will see “Socials” when you scroll down:
Here you can enter your username for the your social profiles. You just need to enter username, not the whole URL. After this do NOT forget to click on “Update” button so these will go in effect on your bio link.
Social link icons will show up at the bottom of your bio link page. You can change color at the top if you need: