Transformer turns ratio
If you can wind some turns onto the transformer without interfering with the winding that are there, add as many as you can comfortably add. Apply 230 volts to the primary and measure the voltage produced by the added winding. Divide the number of added turns by the measured voltage. The result is the turns per volt for any winding. Multiply the calculated turns per volt by the 230 V primary voltage to determine the number of primary turns and by the 24 V secondary voltage to determine the total number of secondary turns.
It would be best to use first measure the applied primary and resulting voltage tor the existing secondary voltage and use those values for the calculations rather than the nominal values. Perform the test with no load connected to the existing secondary winding.