I am not sure what exactly you want to do. What do you want to add force towards? Did you mean forwards?

Another question is also when do you add the force and 90° to left from what?

I assume this:

1. the object you want to add force to is at some angle in the world
2. the object rotates to 90° to the world's left
3. at some time after the rotation you want to add force to it based on the rotation

If that is what you want then you need to:

• specify first what do you measure the angle change from (the original angle) and save it in a variable
• have a vector in the direction you want to add the force when the object has the above-mentioned angle
• when you want to add the force, you need to calculate the difference between the current angle and the saved angle
• rotate the vector based on the angle difference
• add the force in the direction of the vector