Too little imformation to make any kind of recomendation. Their are many different types of mausers and many types of safeties. All different. If you could post some pictures or give more detailed imfo maybe someone on this site could assist you.
I would assume you are talking about a 3 position Military safety. You may have to Cock the bolt, remove it and complete the process to engage the safety. Then take the bolt apart, clean and reassemble. It is usually something silly, but you need to take the bolt apart to find out.
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