No point in building a raised bed if you are just going to fill it with clay!
I understand you weren't the one who did that. If you were building a raised bed on top of clay our advice would have been to take a garden fork or crowbar or something and punch some holes down in to the clay, to promote drainage, then put good soil on top. Perhaps you can still do something like that. I don't know that I would want to mix the clay with your good soil, but you might be able to just dig some of it out and refill the bed with good soil (after making the holes). What are the raised bed sides made of? Do they allow drainage?
You said how tall the beds are (31" inches in American, which is plenty tall), but you didn't say how big or how many. That determines how much work it is worth putting in to it. If you are talking about one meter square plot, you can put the time in to just empty the whole thing and start over. If you are talking about 6 beds double that size, then the project
gets less manageable. ....
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