By design, Guest is a sort of anonymous role and not allowed to have or save any data about itself or in any courses it has access to. Think of it as exactly the same as a web page visitor, since its main use is actually to allow a specific course to made publicly available to anyone over the web to view only. All accesses by any users using Guest are the same user. Even if they could edit this profile, each new guest would overwrite the previous guest profile since the Guest is just one, single predefined view only account.
If you are trying to set it up so that guests can edit their profiles, it tells me that you are really trying to collect data about individual people.
If you really need to tell those people apart from one another, you need some actual user accounts with usernames, etc. So, something like "Visitor1, Visitor2, Visitor3" accounts and hand out the passwords is a common solution, if that is what you need.
Now, if you are trying to do something like have anonymous folks reaching your site to fill out a short survey of questions, such as where they are or where they heard about the site, but are not interested in creating accounts, then one way to do this is use the Feedback module on your front page
in anonymous mode. This allows you to collect survey type data before users even login at all. See https://docs.moodle.org/37/en/Feedback_FAQ#How_can_I_allow_non-logged_in_users_to_give_feedback.3F
for more information on how to set that up. I have done this on a few sites and it works well for that scenario. You can use this in addition to or in place of the Guest account too, depending on what your needs are.
Hope this is helpful.