I’m not 100% sure you can generate a code as a Veteran before the 7 days are up as you are counted now as a new player who accepts a Veterans code.
But if you can it’d be here: https://www.bungie.net/en/Profile/ReferAFriend/254/3106616/O%20E%20l%20f%20e%20n%20a%20O
If you can’t, then you’ll need to find a Veteran and accept their code.
weird that blizzard says this on the help page
"Veteran Player Requirements
A Veteran Player is [b]any player who owns Destiny 2: Forsaken[/b]. Veteran Players may invite New Players for the Refer-a-Friend promotion."
and then
"A New Player is any player who does not own Destiny 2: Forsaken, or has owned it for less than 7 days. Once a player has owned Destiny 2: Forsaken for longer than 7 days, they are no longer eligible to be referred for the Refer-a-Friend promotion. The 7 day eligibility window begins after a New Player first signs in to Destiny 2: Forsaken after purchase."
When I pressed that link it said "You lack the privileges to read or write this data."