I have the simplest triac circuit with one diac, a potentiometer and a capacitor like on this picture https://www.electronics-tutorials.ws/wp-content/uploads/2018/05/power-power24.gif . And the problem is that it fires too early at around 100volt out of 230v. I want it to start conducting at 200-210 volts. How can this be done? What additional components should I use? I use bt136 triac.

 

Welcome to AAC!
Increasing the value of VR1 or C1, or adding a resistor in series with VR1, should do what you want.
What component values are you using?
Incidentally, a mains voltage of 230V (rms) has a peak voltage of about ±320V.

 

Yea I agree that it should be more than 230volts so it should fire at 290volts or similar... I'm using 500k potentiometer and 0.1uF cap.