How to make an iphone backup on a computer inaccessible

Hello, a backup of my iphone is left on a computer of my ex. I don't want it to be accessible. I believe it was an encrypted back-up, but most likely I used the same password as in many other instances and my ex knows it. Is there anyway for me to make this backup no longer accessible? Would for example creating another new encrypted backup on another computer with a new password make the older backup inaccessible? Any tips and help would be greatly appreciated. Many thanks in advance.