Custom textbox to pull a field and allow to add free text

I am fairly new to customizations and I am having trouble creating a specific object. We are upgrading and I have some notes bound to a specific character in our old database created with VB forms.

I created a textbox and bound it to the same character so those notes are displayed in the new system but I am unable to enter any new information into that textbox since it is bound. I would like to be able to see the old notes and then be able to add free text to add on to those notes if that is possible.

I could create 2 boxes one to pull the data and one for new however if it can be done in one that would be the dream. If anyone could point me in the right direction that would be great or even just some ideas would be very helpful.

Thank you for reading this far!