Not clear what you mean.
You might mean using your editor to replace spaces with tabs. Some editors have an indent function that allow you to indent blocks of code which might be easier.
You could try using copy and paste. Try creating a new line with a tab character. You should then be able to copy and paste that in the search and replace box so you can replace a space with a tab.
If you mean you need to programatically replace a space character witha tab character then you need to look at seleting and replacing them as ASCII characters.
What editor are you using? What version of Basic are you using? What do you want to do?