Item ID column has been reset to zero

Morning - I’ve been looking at some automations tying jobs across 2 boards. I have been trying to reference the “Item ID” column - but looking at the settings for the column I changed the display option from “custom key” to “ID Number”, then reverting it back when I realised it would not do what I want. On starting the computer up this morning I find that all the ID’s have reset and started at 001 on the top item only. Is there a way to revert this - we have something like 200 jobs that are files according to this custom ID, and I can’t see a way to fix it! Help! (thanks in advance)