How do I change speed with a variable?

I use platform behaviour in my game i wanna change the speed of character i created global variable and try to write it max speed it wont let me also i try to write it in " " it wont work again how can i use a global variable for character max speed etc.?

In a most basic scenario:

every tick

Object bullet set speed to MyVariable

Pushing it fancy:

System, compare 2 values

object.bullet.speed is not equal to MyVariable

action: object bullet set speed = MyVariable

Then it does not get set every tick, and if you change the MyVariable, it will update the speed.

it is a platform game and i use platform behavior i want to change speed in different circumstance or make an upgrade for player speed, in platform behavior it seems it cant be changed

Ah, you need to update the maxspeed for the platformer I believe.

Compare 2 values: object.platformer.maxspeed is not like MyVariable

etc etc