Help would be appreciated in rectifying error described.
Disclaimer: It is more difficult to describe than to show how to edit Parent-Child Relationship ... perhaps you would find this video helpful: https://youtu.be/8-p8Azz37P4?t=1954 (starts about 32:00 he goes into talking about parent-child relationship a little)
In Family Tree on Chrome browser:
You accomplish this using the pencil icon in the Person> Details view (click on the child you want to Edit and select Person - it defaults to Details view/tab).
Scroll to Family Members section. You should see the child listed under the current Parents.
I assume the mother is staying the same but you want to change to an Unknown father.
It is recommended that you delete relationships only when you are confident the relationship never existed or when the relationship is a duplicate.
Will change the parent child relationship by asking for a different person. It will preserve all of the sources and notes.
I have reviewed the relationships, sources, and notes for these individuals"
In your case - since you do not know the father to replace the current one - you would just Remove the current father. However, my recommendation without knowing particulars - is to choose a different 'Relationship Type'. Although the currently listed father may not be the Biological father - they did occupy the father role at some point apparently.