It seems to be impossible to checkout commits with GitKraken.
As you can see there is no option to checkout older commits, only Cherrypick commit
but I don't know what this is good for.
EDIT: I was able to checkout with another git program (git bash) via console:
Now it looks like this in GitKraken:
GitKraken (as of version 1.7) does not seem to offer a way to get into a detached HEAD mode, and check out a commit directly. Similarly, it will also not allow you to check out a tag (since that would also give you a detached HEAD).
So instead, you will have to create a (temporary) branch first which you can then check out.