So the signal is going to the bicycle’s controller, just altered. Well, if 50% works then a simple digital circuit that counts two and then sends one should work. I can’t help too much with that but there are certainly plenty of prolific circuit folks here who can.

I would do it with a small microcontroller like an ATTiny85 or the like. It’s just a little 8 pin chip that needs only 3 components to operate. The solution then becomes a simple program and the ratio can be arbitrary.

My immediate concern is one of safety and reliability. I have no idea what protection the motor controller has should the new rate allow it to assist to much higher than normal levels. Also, should the circuit fail, you could be stranded in a bad place, or have to pedal your much-too-heavy unassisted bike some distance.

Sir how can I use ATTiny85 to reduce my hall effect signal to 50%

 

An ATTINY "anything" )12, 13, 25, 45, 85, etc. is much more computation power than you are likely to need but it can divide by almost any factor provided that you learn how to do so.

I think Ya'akov's idea is similar to this, which can be accomplished with logic chips:
https://www.electronics-tutorials.ws/counter/count_1.html