Hey @DariusDevitt 
At this time, The Forms will always create a new item when they are submitted – you cannot edit an existing item using a form.
However, I would recommend adding your thoughts and feedback about this form capability to the Feedback Section of the Community so our Product Team can take it into consideration as they make future changes to the platform!
Here is one I found that I think you could vote on and share more about why this is something you and your team need for your workflow: Use Forms to View and Edit as well as Create
If you would like to submit your own feature requests or feedback, you can always add a post or vote and comment on one that already exists here: Feature Feedback and Requests
Our product team takes user feedback very seriously so thank you for taking the time to share your thoughts!
In the meantime, you can always try using the Duplicates and Uniques app like @kolaai mentioned to try and merge related items together.
I hope this helps! Remember to mark as solved if this answers your question 
Cheers,
Jenna