Damp chipboard under vinyl in bathroom

Hi,
First time I have posted on here but need help in finally rectifying an ongoing problem.

I have a ground floor flat and the bath was leaking due to a gap in the seal, the green chipboard underneath was damp and wet and it spread under the vinyl flooring.

The seal has been fixed and the chipboard under the bath has dried out fine and I took up the vinyl flooring to dry out the chipboard. When it had gone from dark to hard I thought it had fully dried so put down the vinyl flooring but checked when the tenants left and it's dark and slightly damp under the vinyl, under the bath is fine.

Can someone tell me the best and quickest way to fully dry out the chipboard as it seems when I lay the vinyl it traps the moisture and it comes to the top again.

There are no windows in the bathroom so leaving the heater on.

Would an industrial heater do the job as I think it's more moisture in the floor and not really wet.

Tenants are due to move in on Thursday!

Thanks

probably needs a dehumidifier running 24/7.

How do you know that the leak was: "due to a gap in the seal"?
How can you be certain that the leaking has indeed stopped?
Pics of above and below the bath might help?

If the chipboard was screwed down then it might be possible to lift it?

Is there an extractor in the bathroom?