[] Replacing text with regular expressions in PHP

[Help] replacing text with regular expressions in PHP now has the following text on the page: ---------------------------- test text A [code = H] ← [/code] test text B [code = H] d0c93d1fac0843a993442688 [help] replacing text with regular expressions in PHP
The page contains the following text:
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Test text
[Code = H] aa622ea28638f1e2f9ebc1c845499ed3 [/code]
Test Text B
[Code = H] d0c93d1fac0843a993421388bd6afd10 [/code]
Test text C
[Code = H] 0F3D2A4C5BCA48F0B9E8E4564DEFB127 [/code]
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In php, how can I use a regular expression to find the text above "starting with [code = H] and ending with [/code]" and replace it with another text.
I'm a beginner in php. thank you.

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What is another piece of text?
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PHP code

$ S = <TXT test text A [code = H] aa622ea28638f1e2f9ebc1c845499ed3