Hi,
I am not quite sure what you mean with 'character string', maybe my English is too bad.
But if you want to find a specific combination of characters say "water" or "5.000" which are definitely in the sheet, then tap on tools (top right corner) and select "find" (could be a different wording - I use the German version) and key in your search string/term. Works with text and numbers.
Does this make sense to you?
Knut