Had same problem, just go to the Samsung members and click on the alert sign 🔔 at the to of the page, it should take you to; Notices, and the first notice will tell you to claim on wearable. Hope that helps
i have just got samsung s20 5g and down loaded samsung benefits on new phone where it came up with how to claim..on site it says you have 30 days after purchase date to claim watch after purchasing qualifying phone.The phone must be purchased by 30th sept but you have 30 days from your purchase date to submit a claim for watch. ie if you purchased phone on 30th September your claiming expiry date is 27th October . Long winded answer but hope it helps.
I'm presuming you need to actually have the handset first and load Samsung Members from the device and go to the alert and notices section. My Samsung S20 5g is arriving tomorrow so will check back here with results.