Hi Shreeshail,
Looks like your speaking with our team via email, but wanted to share that support here as well for anyone visiting with the same question.
You can activate your credits from your Retool account by upgrading to any paid plan (this can be done by visiting Settings > Billing or just clicking Upgrade in the top right on the homepage). Please note that any unused credits will expire in 1 year, so feel free to invite additional teammates to make full use of your credits. Also, Startup credits only work on monthly plans, so be sure to make sure this is chosen before you subscribe!
Admins of Cloud orgs can check out the remaining credits by going to Settings -> Billing and scrolling to the bottom of the page.
Let me know if that helps or if there's anything else I can assist with. 