Dependent fields - enable/disable fields based on my choice on an adjacent field

I suggest using a Dynamic Form Rule.  There is a tab for that when you customize the form.

When [Choice] is not equal to NEW
Make Read only [Adjacent]
Change Adjacent to (blank)

 and set that rule to fire all the time, so uncheck the checkbox at the very bottom of that rule.

Hey, thanks for the replay, I am very new to this, I have learned the basics here but I need this feature very urgent, I don't know where to set rules from, where should I go to set dynamic form rule?

thanks

no problem,
When you are viewing a record on a form, look for Customize this form at the top right.

Then look for the tab called Dynamic Form Rules.

https://help.quickbase.com/user-assistance/form_rules.html