How I use backslash because this sign is not available in my smartphone ?

Answer 1

if you can't find it on your keyboard, you have 4 options:
A) Use android default keyboard
B) Install another keyboard
C) google backslash char and copy paste it where necessary
D) Copy the backslash available in the custom symbols bar from SL Code Playground and paste it where necessary.

Answer 2

the sign should be available under the numbers/symbols option, possible on "page" 2 of that section

Answer 3

thanks