Thanks for the suggestions people.
Tha tire is good for the rim.
I tried the dilute washing up liquid at the first attempt; tried more of it on subsequent attempts, and inflating up to 5 bars, (its rated maximum.)
The fit has improved a bit, but still not seated pertectly.
The tyre had been folded when new. I had left it on a flat surface for 2 weeks before fitting. I wonder if this is the cause?
It is on a QNT trike. The ride is not as smooth as it could be, and the reflective bead on the tyre is in my view much of the time.
Could live with it. Would be satisfying to sort it out perfectly.