Search payload and redirect to payload value

Hi

 

 

I managed to resolve this apart from this line:

 

 

set content "'document.forms.submit();'"

 

 

 

I want to add in [0] like this in a string:

 

 

 

set content "'document.forms[0].submit();'"

 

 

 

but its not allowing me.

 

 

Any ideas?