Remove parts of a tag field

Newbie here I a question about removing characters to the right of standard expression

George Gently S7 D1 E1_Title1

I want to remove everything to the right of "_" and including it...

I am sure this is a simple procedure but don't know what to pick this program can be so powerful if you can understand all the commands...!

Thanks,.
John G

You don't tell us in which tagfield this content is.
If it is not the filename you can use an action of

Type: Guess Values
Source Format: %the tagfield where this is content%
Guessing Pattern: %the tagfield where this is content%_%dummy%

Yes, shows you how new I am it is in the _FILENAME field. I am actually using this for rewriting MP4 files. I know it probably isn't meant for it but it does work I have done simple things like copy _FILENAME to Title name. This one has me stumped so for such a long time since responding. I didn't remember I had used this site to post this.

So you want to just change the filename only?
Take the Coverter Filename -> Filename.
Old filename pattern: %1_%2
New filename pattern: %1

Sorry for the slow response I couldn't find my login credentials..
Anyway. What I want to do is this as an example the file name is
The Girl in the Spider_Title1.MP4
I want to remove all the characters to the right and including the "_" but keep the ".MP4" and not leave a space before the period either.
Does this make sense?
so the end result I would like is
The Girl in the Spider.MP4
I hope this helps for some one to help me. I know it is probably a simple few steps but I still haven't grasped how the expression work in MP3Tag.
Thanks,
John

The solution has already been posted in

Hello, I don't understand the COVERTER FILENAME -> Filename which one of the dropdown is this? Sorry I told you I am new and not too familiar with all the commands. Sorry for being a newb but I want to learn

john

it's in the 'convert' menu (or ALT 3)