When l try to log into ArcGIS Pro it does not accept because my ArcGIS Online account is a public account.
How can l fix this problem?
I am assuming that the message you are seeing is:
Your account could not be used to authorize ArcGIS Pro because it is an ArcGIS Public Account.
If you don't have an ArcGIS organization account, you can sign up for an ArcGIS free trial that includes an ArcGIS Online organization and access to ArcGIS Pro, ArcGIS Pro extension products, and other apps.
ESRI support is https://support.esri.com/en/contact-tech-support