If you want to completely overwrite the trunk file with a forked file, you can delete the trunk file and then make a copy of the branch (simple and radical)
svn delete https://web/trunk/text.cpp -m "delete trunk file" svn copy https://web/branches/tt_branch/text.cpp
If you want to do something less absolute try using svn merge
svn merge https://web/branches/tt_branch/text.cpp https://web/trunk/text.cpp
which asks you to resolve potential conflicts, if you do not want to resolve conflicts, try the following:
svn merge --accept theirs-full https://web/branches/tt_branch/text.cpp https://web/trunk/text.cpp
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