vim tabs/spaces FAQ: How do I convert vi/vim tabs to spaces?
You can convert tabs to spaces in vim using the usual vim search and replace command. Specifically, this vim "tabs to spaces" command is all you need:
In short, this command can be read like this:
Regarding that last line, if you really just want to convert the first tab on each line to spaces, just use the same command, but omit the 'g' at the end, like this:
That's all you need to convert tabs to spaces in vim.