Multi Checkbox can not be changed after selected

Hello,

I’m running into a problem, where after selecting one option from the Multi Checkbox, the customer can not change his mind and select the other option. This field is required by every customer and only one option can be selected, but I want my clients to be able to change their mind in case they select the wrong option at first.

Can this be adjusted please?
Thank you

The page I need help with: [log in to see the link]