1: Please click the site (https://bard.google.com) on your PC browser. And log in your google account. As the bard site is still under experience period so you need to join the waitlist. Generally it will take 2-3 days for you to get an email to use.
2: As you have got the email to use. Please click the site (https://bard.google.com) on your PC again and then click three dot on the top right corner of this website>>More tools
>>Developer tools>>Application>>and click cookies on the left column and find cookie named as"Secure-1PSID" to copy its value is Token.