Convert Filename-Tag but truncate characters

I want to convert Filename-Tag... how do I truncate the first few characters?

Before (filename): ABC_Filename_123.mp3
After (track title): Filename_123

I wonder which title has an underscore in it ...

Awesome, thank you. What should I use if the underscore was not there:

Before (filename): ABCFilename123.mp3
After (track title): Filename123

then try the same without underscore.
Use %dummy% (and all the text constants like parenthesis) for every bit that you do not want.
The preview will show whether you are on the right track.

Doesn't work, how do I trim a certain number of characters (from beginning or the end) if the text is different on every filename

couldn't you give a real example?
You don't say what

Otherwise: please use the search function as there are numerous threads that deal with this problem. "cut" and "delete" would be suitable search words,

Try to use Actions ► New ► Remove (Number of your desired Chars) leading chars by Regex. Here is the Example: