Hello,
You can reset as Admin a password for a general Microsoft Guest User (that is commonly generated into Azure Active Directory from here (https://entra.microsoft.com/).
Seeing the screenshot, you can follow the steps to identify the section where you can apply this function:
- Go to https://entra.microsoft.com/ Home page.
- Open the Users section, in the left column.
- Digit the name of the Guest User that you want to manage.
- You'll be redirected in his Overview main page (you'll recognize it, because his first/last Name will be showed on the top with big characters
- On the top menu bar of his Overview, click on "Reset Password"
An External User invited by your organization can't change a password by himself.
Microsoft doesn't allow to obtain a copy of the password chosed by the Guest user.