This is a relatively straightforward question and similar questions have been asked before so we aren't going to re-invent the wheel for you. Do a search for 'Batch find replace' and you will see lots of threads with code. A few minor changes will allow those macros to work on your specific requirements.

If you get stuck, post back here with a description of your sticking point, the code you are using and include a link to the original thread where you got it from.

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Andrew Lockton
Chrysalis Design, Melbourne Australia