How to resolve the current index first?

 The error implies that there occurs a merge conflict and you won’t be allowed to shift to another branch without fixing the error. The message depicts that a merge failed. The error happens when you have shared the earlier master branch with anybody. This raises issues, because the history of the branches when shifted, a new history would be written. You wish to merge your branch into master keeping the file versions in the topic branch. This can be done by the below-mentioned steps:

# switch to the topic branch:
Git checkout branch

Make a merge commit, that resembles as if it is merging from the master branch. However, in reality it is disregarding everything from the master branch

Git merge -s ours master
# switch back to the master branch:
Git checkout master
Now emerge the topic branch to the master branch. 
Things can be reset to normal by the following code:
Git reset – merge 
You can also try another method.

Ensure that the changes are committed. This is a nice habit that saves you from various hassles. Assure there are no uncommitted changes prior to the checkout

# stage all the changes for commit
$ git add.
# commit
$ git commit -m ‘commit message’
Discard the merge and get back to the earlier level.
# cancel the emerge
$ git reset – merge
# OR
# reset all the changes back to the last
# Note: This cannot be reverted!
$ git reset – hard HEAD
Fix the reported conflicts
Open the files having conflicts and commit the changes.
# CONFLICT (content) : Merge conflict
# open the file in an editor of your choice
$ vim/path /to / file_with_conflict
#repeat for every file that ahs a conflict
$ git commit -a -m ‘commit message’
Incase of a git checkout, there’s another way as below:
# force - change a branch
$ git checkout -f TARGET

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