How to edit the word "Search" on search area

how to change this one?
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Spoiler:

BTW.., my forum version is phpbb3

I really think you can't edit that word unless you press backspace.

There is no part in the admin panel saying you can change that word.

You can't change it.

I remember doing something like this with a 'Search' HTML code before when I was looking it up. Try to google this information up and you will probably find what you need.
However, you cannot edit the Search menu from where it is defaulted at it's position- in other words, there is no access to it if you want to edit it.