Fluent Forms WP Plugin - Create a unique number for each submission

Hi there,

I'd like to know how to generate a unique string that can be used as a reference number for each entry submission in Fluent Forms? I need something like ORDER0001 and make it consecutive (ORDER0002, etc). One for each entry submission.
Apologies if it's an easy question, I'm not an expert in Fluent Forms.
Many thanks!