I have add *.sqlite3 to my .gitignore_global file:

When I run git status in my terminal there still have db.sqlite3 listed as modified:

How can I ignore my SQLite file?
I have add *.sqlite3 to my .gitignore_global file:

When I run git status in my terminal there still have db.sqlite3 listed as modified:

How can I ignore my SQLite file?
I see three issues here:
.gitignore_global isn't a standard Git ignore file. If you haven't told Git about it it will have no effect. Something like git config --global core.excludesfile <file> can be used to add a global ignore file.
Your screenshot actually doesn't show *.sqlite3 in your ignore file. You'll have to add that, or a pattern like it.
Finally, and most importantly, Git's ignore system doesn't prevent tracked files from being modified. It only prevents files from being tracked in the first place. Your screenshot shows db.sqlite3 as being modified, not new.
You can tell Git to stop tracking the file with git rm --cached db.sqlite3, then commit. This will leave the file in place, but remove it from the repository. Once that's done, and the previous two issues have been dealt with, your file should be ignored.
I tried this command, and it did ignore changes in db.sqlite3:
git update-index --assume-unchanged db.sqlite3
db.sqlite3 shouldn't be in your repository at all. In that case it should be removed, e.g. with git rm --cached db.sqlite3, and that change should be committed.