To open an RBXL file you need 2 things

1,you need Roblox Studio to open the file, if you don’t have that then go press the “create” bottom on the platform and if it says you wanna download it or not CLICK DOWN LOAD.

2,next you wanna make sure to downloaded the RBXL or RBXM (for a RBXM you gotta drag the file into Roblox from file manager or from what ever pc you have I guess) when you have the RBXL selected right click on it and open it thru Roblox studio then congratulations you mess around with it for as long as you want