Well you'll need to have stashed £15+ worth of clubcard vouchers by then, and the rewards are on the Tesco Clubcard site... https://secure.tesco.com/clubcard/boost/family-friends-railcard/UK-002022.prd
I already ordered the Railcard but I have £1.50 clubcard voucher how can I benefit if I wanted to buy another for next time
Tip: If you have some Tesco Clubcard £ you can use it to buy Railcards - typically at double-value/"half-price" ie £30 card for £15 Clubcard, although clearly this HUKD 20% saving to £24 makes the Tesco deal less attractive, and also you can use the Clubcard at triple value on rail travel via redspottedhanky (albeit with a £1 per booking fee).
It'll be posted to you.
Thank you :)