"Fiddly, but don't give up!"
I agree with your previous reviewers that some instructions would be very useful. Yes, this is a very fiddly product, but I have found a solution... ...I use wide (5cm) sticky tape to hold the letters in place, before inverting the plate to insert into the silicone ring. Although not ideal, this works well enough to use the stamp. A bit of inventiveness is necessary, but it would be a shame not to be able to use the stamp. Perhaps the design needs to be modified?