I have a folder consisting of approximately 500 txt files. The names of these txt files were recorded as 001.txt, 002.txt….478.txt.

The contents of these files are as follows

cd C:UsersAnarShycafeintest
unimportant words here >> 1mayis.txt
unimportant words here >> 1mayis.txt
unimportant words here >> 1mayis.txt

What I want to do is to replace the 1mayis.txt text in these files with the name of that file.
For example, I want to automatically convert the content of the 001.txt file to the following.

Before

cd C:UsersAnarShycafeintest
unimportant words here >> 1mayis.txt
unimportant words here >> 1mayis.txt
unimportant words here >> 1mayis.txt

Later

cd C:UsersAnarShycafeintest
unimportant words here >> 001.txt
unimportant words here >> 001.txt
unimportant words here >> 001.txt

In summary, I want to replace the word 1mayis.txt in 500 txt files with the original name of the file it is in.
I tried to change the files one by one with ctrl+H, but it took an extremely long time.