1. If you are using Mobile Guard, go to :
Steam > Settings > Account > Manage guard > Get backup codes > And Paste 5-20+ Backup Codes (depending how large is your order) in the Field Above.

2. If you are using Email Guard, please turn it off. By going in to settings > disable steam guard > and Confirm from the Email.  Make sure that you have pressed the “Confirm Link” otherwise Guard will still be ON.

❗ Steam Guard Backup Codes are not used for TRADING / Steam Credentials Change. Please test it your self to make sure that the backup codes are only used for loging into the account. This means that nobody can change or accept trades from via these codes. Only you manage everything from your Phone.