By using CSS You can control the button.

button#back { display: none; }

If it's required only for page . You can add it in customhtml.

For entire application you can add it userview custom CSS or settings custom css

May I know where should i be placing that code?
because i tried to put in customhtml it doesn't work 

maybe can you show me the screenshot

Hi Tarek, 

if you want to hide the back button for only that form then add a custom html field in the form and paste the following code:

<style>
    #cancel {
    display: none !important;
}
</style>

In the above code cancel is the ID of the button and we are selecting it based on ID using #cancel and applying CSS changes to it. You might want to check the ID of the button and change it accordingly based on the buttons you want to hide / show. 

Additionally if you wish to hide this button for all forms you need to put the same code in your ui builder → Settings → Find custom css and put the code without the style tag. Hope this helps.