How can I decode this phone?

Not sure why you marked your comment that you are having a hard time as the Best Answer above, but you are not going to be able to get anywhere with the phone unless you can get the Apple ID and Password that was used by your sister (or whoever it was that set up the phone originally).

Do you have that information?

The phone is pretty much useless otherwise.

Then answer the question that we asked.

Do you have the Apple ID and Apple ID Password of the person who set up the phone originally?

If you do, we can help. If you don't, no one can help.

If the phone is activation locked, only the owner of the account used to lock it can remove the lock.

Hanesslewion wrote:

my sister give me this phone but I’m trying to decode but it not going because her iCloud was locked by my I miss it so it’s giving my hard time.

Can we assume you have already solved your tech support issue by merely posting the text above?