Wa Alaykum Assalam and thank you for your question.

If a non-Muslim gives you salam then reply with the same salam as Allah tells us in his book what means:

{When a (courteous) greeting is offered you, meet it with a greeting still more courteous, or (at least) of equal courtesy. Allah takes careful account of all things.} (Al-Nisaa 4:81)

If we can develop and maintain relationships with non-Muslims based on mutual love and respect, then this is a great accomplishment.

Only Allah guides whom He wills to Islam. It is our duty to convey the message and beauty of Islam to others in whatever ways possible.

I hope this helps answer your question.

Salam and please keep in touch.