I've recently encountered this problem:

git -c diff.mnemonicprefix=false -c core.quotepath=false checkout – source/VersionInfo.cs
fatal: Unable to create 'C:/Projects/xyz/.git/index.lock': File exists.

If no other git process is currently running, this probably means a
git process crashed in this repository earlier. Make sure no other git
process is running and remove the file manually to continue.

Just not to blame SourceTree : It wasn't his fault

But I would like to have a little helper button: "Delete index.lock" or "Free lock" or even a Force option might be helpful. Everything I want is remaining in the UI of SourceTree and don't open the stupid Console typing this: >del .git\index.lock.

Can youo help me?
Thanks
Marcel