How to open script with other script?

Hello, i have been just building a game not thinking about a menu and things like that. Now the game is finished i wanted to make a start menu, but instead of adding it to the script of the game i want to make a second script with a button and if the button is pressed i want to trigger the other script so the game will be build.
I got the second script with buttons and everything but i don’t know how to trigger the game script.
I named the game script Builder and it’s located in the assets list.
I tried to Google for a solution but i couldn’t really find it, i might have used the wrong search terms but i really kinda need a solution.
Thx for all replies in advance!

You could add the second script when the button is pressed.