I also think so Agx, but maybe there is a trick to do it the right way. The chain has a lot of grease so I do not want to mess up my hands to much when there is a simple way to solve it
I have a manual for my De Vere 5108, I did scan part of it for someone on this forum a few years ag. the 504.507, and 5108 all use exactly the same two part column and base.
If I can't find the scans I can copy the relevant section again later today.
Is it the floor standing 507 ? You may well need to remove the column and then get the chain back over the cogs, it is a little messy because of the grease. I've done this two or more likely 3 times since buying the enlarger second hand and moving it twice. It's not difficult just slightly awkward to get at. You can't do it while the enlarger's assembled.