GrowDash uses one password flow for both scenarios — locked out, or just want to change it while logged in. There's no "enter your old password" form; it's always an emailed link.
If you're locked out
On the sign-in page, click "Forgot password" and enter your email. You'll see the same message either way — whether or not that email has an account — so you can't use this to check if someone else has signed up.
If you're signed in and just want to change it
Go to your Profile page and use "Send password reset email" — it triggers the exact same emailed link.
Using the link
Click the link in the email, set a new password, and you're redirected to sign in. The link is only valid for a limited time and works once — if it's expired, just request a new one.
Note
GrowDash accounts are set up for you when you sign up — there's no self-service account creation — but password resets work the same regardless.